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Glycolysis, Gluconeogenesis, and PPP (1D) - Bio & Biochem

  1. A physiology study (150–250 words) examined hepatocytes exposed to high citrate, modeling abundant mitochondrial export of acetyl-CoA equivalents in the fed state. Without changing insulin signaling, citrate addition decreased conversion of fructose-6-phosphate to fructose-1,6-bisphosphate and reduced lactate production. ATP levels were high. Regulatory node: Fructose-6-phosphate →PFK-1\xrightarrow{\textit{PFK-1}} Fructose-1,6-bisphosphate Which outcome is most consistent with citrate-mediated regulation at this step?
    Answer: Decreased glycolytic flux due to allosteric inhibition of PFK-1 under high-energy conditions This question tests allosteric regulation of glycolysis by energy signals. Citrate inhibits PFK-1 to slow glycolysis when energy is abundant, preventing excess pyruvate production. In these hepatocytes, high citrate decreases PFK-1 activity, reducing fructose-1,6-bisphosphate and lactate output under high ATP. Choice B is correct because it describes decreased glycolytic flux via citrate inhibition in high-energy conditions. Choice A fails by incorrectly calling citrate an activator, misunderstanding its feedback role. In similar questions, identify feedback inhibitors from downstream pathways. Check if the condition signals energy surplus or deficit.
  2. Erythrocytes from a cohort with chronic hemolysis showed markedly reduced NADPH/NADP+^+ ratio at baseline. Sequencing identified a missense variant in glucose-6-phosphate dehydrogenase that decreases catalytic efficiency but does not change enzyme abundance. Under an oxidant challenge ex vivo, cells exhibited increased methemoglobin formation. Which prediction is most aligned with the described mutation in the oxidative phase of the pentose phosphate pathway (PPP)?
    Answer: Decreased NADPH availability leading to impaired regeneration of reduced glutathione (GSH) This question tests understanding of the pentose phosphate pathway's oxidative phase and its role in generating NADPH. Glucose-6-phosphate dehydrogenase (G6PD) catalyzes the rate-limiting step of the oxidative PPP, converting glucose-6-phosphate to 6-phosphogluconolactone while reducing NADP+ to NADPH. A mutation decreasing G6PD catalytic efficiency would reduce NADPH production, impairing the cell's ability to regenerate reduced glutathione (GSH) from oxidized glutathione (GSSG). This leaves erythrocytes vulnerable to oxidative damage, explaining the increased methemoglobin formation under oxidant challenge. Choice A incorrectly suggests increased NADPH generation, while choice C wrongly claims the PPP produces ATP. For PPP questions, remember that the oxidative phase generates NADPH (not ATP) for reductive biosynthesis and antioxidant defense.
  3. In hepatocytes, investigators pharmacologically increased cytosolic citrate concentration while holding ATP and AMP constant. They observed a rapid decrease in glycolytic flux and a rise in upstream hexose phosphates. Which outcome is most consistent with citrate-mediated regulation in this setting?
    Answer: Allosteric inhibition of phosphofructokinase-1, decreasing fructose-1,6-bisphosphate formation This question tests understanding of citrate as an allosteric regulator of glycolysis. Citrate is a key allosteric inhibitor of phosphofructokinase-1 (PFK-1), the committed step of glycolysis that converts fructose-6-phosphate to fructose-1,6-bisphosphate. High cytosolic citrate indicates sufficient biosynthetic precursors and energy status, signaling to decrease glycolytic flux. When citrate inhibits PFK-1, fructose-1,6-bisphosphate formation decreases, causing upstream hexose phosphates (glucose-6-phosphate and fructose-6-phosphate) to accumulate. This regulatory mechanism prevents excessive glycolysis when citrate cycle intermediates are abundant. Choice B incorrectly states citrate activates PFK-1, choice C wrongly connects citrate to G6PD regulation, and choice D confuses the effects on different pathways. To identify allosteric regulation patterns, remember that citrate, ATP, and H+ inhibit PFK-1, while AMP, ADP, and fructose-2,6-bisphosphate activate it.
  4. A tumor cell line is engineered to overexpress cytosolic pyruvate kinase (PK) while maintaining the same glucose uptake rate. In culture, oxygen is sufficient, but the cells exhibit increased lactate secretion and decreased incorporation of glucose-derived carbon into biosynthetic pathways. Which outcome is most consistent with increased PK activity in this context?
    Answer: Increased net ATP generation at the phosphoenolpyruvate step, with increased pyruvate availability for lactate formation This question tests understanding of pyruvate kinase (PK) regulation and metabolic flux control. PK catalyzes the final ATP-generating step of glycolysis, converting phosphoenolpyruvate to pyruvate. Overexpressing PK increases the conversion of PEP to pyruvate, generating ATP and increasing pyruvate availability. With constant glucose uptake but increased PK activity, more glucose carbon flows through glycolysis to pyruvate rather than being diverted to biosynthetic pathways. The excess pyruvate is converted to lactate even with sufficient oxygen (aerobic glycolysis or Warburg effect), explaining increased lactate secretion. Choice A incorrectly suggests PK overexpression decreases its own activity, choice B wrongly connects PK to PPP regulation, and choice D mistakenly identifies PK as a gluconeogenic enzyme. To analyze metabolic engineering effects, trace how altered enzyme activity affects substrate availability for competing pathways.
  5. During a 24-hour fast, a subject's plasma glucagon is elevated and insulin is low. A liver biopsy specimen is analyzed ex vivo with saturating substrates. Investigators specifically increased the activity of fructose-1,6-bisphosphatase (FBPase-1) via a small-molecule activator, without directly altering other enzymes. Which prediction is most aligned with increased FBPase-1 activity under fasting-like hormonal conditions?
    Answer: Increased hepatic conversion of fructose-1,6-bisphosphate to fructose-6-phosphate, favoring net glucose production This question tests understanding of fructose-1,6-bisphosphatase (FBPase-1) function in gluconeogenesis. FBPase-1 catalyzes a key gluconeogenic step, converting fructose-1,6-bisphosphate to fructose-6-phosphate, which opposes the glycolytic PFK-1 reaction. During fasting, elevated glucagon and low insulin favor gluconeogenesis to maintain blood glucose. Activating FBPase-1 would increase the conversion of fructose-1,6-bisphosphate to fructose-6-phosphate, driving gluconeogenic flux toward glucose-6-phosphate and ultimately glucose production. This explains the increased hepatic glucose production in choice A. Choice B incorrectly describes FBPase-1 as catalyzing a glycolytic step, choice C wrongly links FBPase-1 to pyruvate kinase regulation, and choice D confuses FBPase-1 with G6PD of the PPP. When analyzing metabolic scenarios, identify whether conditions favor anabolism (fed state) or catabolism/gluconeogenesis (fasted state) to predict enzyme activity patterns.
  6. In a hypoglycemia model (150–250 words), isolated liver cells were supplied with alanine as the primary carbon source under high glucagon. Investigators observed increased conversion of alanine to pyruvate and then increased glucose output. When pyruvate carboxylase was inhibited, glucose output fell and pyruvate accumulated despite adequate ATP. Reaction context: Pyruvate + CO2_2 + ATP →pyruvate carboxylase\xrightarrow{\textit{pyruvate carboxylase}} Oxaloacetate Which prediction is most aligned with inhibition of pyruvate carboxylase in this setting?
    Answer: Reduced gluconeogenesis from alanine because oxaloacetate supply for downstream steps is limited This question tests the entry step of gluconeogenesis from pyruvate. Pyruvate carboxylase converts pyruvate to oxaloacetate, essential for gluconeogenesis from lactate or alanine. In this model, inhibition of pyruvate carboxylase limits oxaloacetate, reducing glucose output and causing pyruvate buildup. Choice D is correct because it explains reduced gluconeogenesis from alanine due to limited substrate supply. Choice B fails by suggesting increased flux, ignoring the block at this mitochondrial step. For similar questions, map precursor entry points in gluconeogenesis. Verify if inhibition leads to upstream accumulation and downstream depletion.
  7. In isolated skeletal muscle fibers, investigators increased cytosolic citrate by perfusing a membrane-permeable citrate ester while keeping glucose and oxygen constant. Within minutes, fructose-1,6-bisphosphate decreased and upstream intermediates accumulated. The authors attribute the effect to allosteric inhibition of PFK-1 by citrate, reducing commitment to glycolysis: F6P --(PFK-1)→ F1,6BP Which outcome is most consistent with increased citrate-mediated inhibition of PFK-1 in these muscle fibers?
    Answer: Increased glucose-6-phosphate availability for glycogen synthesis due to slowed glycolysis This question tests understanding of citrate's role as an allosteric inhibitor of phosphofructokinase-1 (PFK-1). Citrate, produced in the citric acid cycle, signals adequate cellular energy and inhibits PFK-1, thereby slowing glycolysis at its committed step. When PFK-1 is inhibited, conversion of F6P to F1,6BP decreases, causing upstream metabolites including G6P to accumulate. This accumulated G6P becomes available for alternative pathways including glycogen synthesis. The correct answer (C) accurately describes increased G6P availability for glycogen synthesis due to slowed glycolysis. Option A incorrectly predicts increased glycolytic flux when citrate actually inhibits it. When analyzing metabolic regulation, remember that citrate acts as a feedback inhibitor signaling energy sufficiency, redirecting glucose away from catabolism toward storage.
  8. A skeletal muscle biopsy study measured enzyme activity before and after a brief high-intensity sprint. Post-exercise samples showed increased AMP and decreased ATP, with increased conversion of glycogen-derived glucose-6-phosphate through glycolysis. The investigators emphasized a regulatory step that commits glucose to glycolysis. Which outcome is most consistent with increased activity of PFK-1 in exercising muscle?
    Answer: Increased fructose-1,6-bisphosphate formation with increased downstream production of pyruvate/lactate This question tests understanding of PFK-1 regulation during exercise. During high-intensity exercise, ATP is rapidly consumed, leading to increased AMP and decreased ATP levels. AMP is a potent allosteric activator of PFK-1, while the decreased ATP removes allosteric inhibition. This metabolic state strongly activates PFK-1, increasing conversion of fructose-6-phosphate to fructose-1,6-bisphosphate and driving glycolytic flux to rapidly regenerate ATP. The increased downstream production of pyruvate and lactate follows from this enhanced glycolytic flux. Choice A incorrectly claims AMP inhibits PFK-1, while choice D wrongly inflates the ATP yield. For exercise metabolism questions, remember that low energy charge (high AMP/ATP ratio) activates glycolysis through PFK-1 to rapidly restore ATP levels.
  9. In a cell-free cytosolic system supplied with glucose-6-phosphate (G6P), investigators compared NADPH production under two conditions: (i) high NADP+^+ and (ii) high NADPH. They observed that increasing NADPH strongly reduced flux through the first oxidative PPP step catalyzed by glucose-6-phosphate dehydrogenase (G6PD). The monitored reaction was: G6P + NADP+^+ --(G6PD)→ 6-phosphogluconolactone + NADPH + H+^+ Which outcome is most consistent with increased oxidative PPP flux in condition (i)?
    Answer: Increased NADPH generation, supporting reductive biosynthesis and antioxidant defense This question tests understanding of product inhibition in the oxidative pentose phosphate pathway. Glucose-6-phosphate dehydrogenase (G6PD) catalyzes the rate-limiting step of the oxidative PPP, converting G6P and NADP+ to 6-phosphogluconolactone and NADPH. This reaction is strongly inhibited by its product NADPH through competitive inhibition with NADP+. Under condition (i) with high NADP+ and low NADPH, product inhibition is minimal, allowing maximal G6PD activity and NADPH generation for reductive biosynthesis and antioxidant defense. The correct answer (D) accurately describes increased NADPH generation supporting these functions. Option B incorrectly states that NADP+ inhibits G6PD when it is actually the required substrate. To predict PPP flux, remember that the NADPH/NADP+ ratio controls oxidative PPP activity through product inhibition of G6PD.
  10. A tumor cell line was engineered to overexpress pyruvate kinase M2 (PKM2) locked in a high-activity tetrameric state. Under normoxia with abundant glucose, the modified cells showed decreased accumulation of upstream glycolytic intermediates used for biosynthesis. Which outcome is most consistent with increased pyruvate kinase activity in this context?
    Answer: Increased conversion of PEP to pyruvate with increased ATP generation at the pyruvate kinase step This question tests understanding of pyruvate kinase's role in glycolysis and metabolic flux. Pyruvate kinase catalyzes the final ATP-generating step of glycolysis, converting phosphoenolpyruvate (PEP) to pyruvate. When PKM2 is locked in its high-activity tetrameric state, it efficiently converts PEP to pyruvate, generating ATP and preventing accumulation of upstream glycolytic intermediates. This increased flux through the terminal glycolytic step reduces the availability of intermediates for biosynthetic pathways (like serine synthesis from 3-phosphoglycerate). Choice A incorrectly suggests PEP accumulation, while choice D wrongly connects pyruvate kinase to the PPP. For metabolic flux questions, remember that increasing enzyme activity at a regulatory step pulls substrates through that reaction, depleting upstream intermediates.
  11. A liver-directed gene therapy (150–250 words) increased expression of glucose-6-phosphatase in hepatocytes. In the fasting state, treated animals showed increased plasma glucose and decreased hepatic glucose-6-phosphate (G6P) levels compared with controls; glycolytic lactate production decreased. The investigators emphasized the terminal step of gluconeogenesis/glycogenolysis. Key step: G6P →glucose-6-phosphatase\xrightarrow{\textit{glucose-6-phosphatase}} Glucose + Pi_i Which prediction is most aligned with increased glucose-6-phosphatase activity in liver during fasting?
    Answer: Increased hepatic glucose export due to enhanced conversion of G6P to free glucose This question tests the terminal step of hepatic glucose release. Glucose-6-phosphatase hydrolyzes G6P to free glucose, enabling export during fasting. In this therapy, increased enzyme activity depletes hepatic G6P, enhancing glucose output and reducing glycolysis. Choice A is correct because it explains increased export via efficient G6P conversion. Choice B fails by suggesting trapping as G6P, confusing the enzyme's hydrolytic function. In similar questions, identify unique hepatic enzymes for glucose homeostasis. Check for effects on intracellular metabolites and plasma levels.
  12. A nutritional intervention study (150–250 words) compared liver metabolism after a carbohydrate-rich meal vs after an overnight fast. After the meal, hepatic glycogen synthesis increased and plasma lactate rose modestly. The investigators noted decreased net hepatic glucose production and proposed that gluconeogenic flux was acutely suppressed at a key step sensitive to fructose-2,6-bisphosphate (F2,6BP). Node: Fructose-1,6-bisphosphate →FBPase-1\xrightarrow{\textit{FBPase-1}} Fructose-6-phosphate Based on the scenario, which metabolic shift would be expected in the postprandial state?
    Answer: Decreased FBPase-1 activity due to higher F2,6BP, reducing gluconeogenic contribution to glucose output This question tests postprandial suppression of gluconeogenesis. In the fed state, elevated F2,6BP inhibits FBPase-1, reducing gluconeogenic flux and net glucose production. After the meal, decreased hepatic glucose output reflects FBPase-1 inhibition, favoring glycogen synthesis. Choice D is correct because higher F2,6BP decreases FBPase-1 activity, suppressing gluconeogenesis. Choice B fails by stating insulin activates FBPase-1 via AMP, confusing regulators. For similar questions, contrast fed and fasting regulatory states. Verify if the shift reduces unnecessary glucose production.
  13. A fasting-state mouse model (150–250 words) was engineered to express a liver-specific variant of fructose-1,6-bisphosphatase (FBPase-1) that is resistant to inhibition by AMP. During a 16-hour fast, hepatic ATP and AMP levels were measured and found to be low ATP/high AMP compared with wild-type, yet plasma glucose remained elevated. No changes were observed in glucagon receptor signaling. Reaction context: Fructose-1,6-bisphosphate →FBPase-1\xrightarrow{\textit{FBPase-1}} Fructose-6-phosphate (gluconeogenesis) Which prediction is most aligned with the described mutation?
    Answer: Increased hepatic gluconeogenic flux despite high AMP, promoting continued glucose output during fasting This question tests the regulation of gluconeogenesis by allosteric inhibitors at key enzymes. AMP inhibits FBPase-1, a rate-limiting enzyme in gluconeogenesis, to prevent futile cycling during low-energy states. In this mouse model, the AMP-resistant FBPase-1 mutation allows gluconeogenesis to proceed despite high AMP, maintaining glucose output. Choice B is correct because the mutation bypasses AMP inhibition, increasing gluconeogenic flux and sustaining plasma glucose during fasting. Choice A fails due to misunderstanding that high AMP would still inhibit the mutated enzyme, but the variant is resistant. In similar questions, check for mutations altering allosteric sites and their impact on pathway flux. Verify if the change favors the pathway's continuation under inhibitory conditions.
  14. A metabolite clamp study (150–250 words) in hepatocytes maintained high acetyl-CoA while varying pyruvate availability. Under high acetyl-CoA, conversion of pyruvate to oxaloacetate increased, supporting glucose production from lactate. The investigators focused on acute allosteric regulation at the mitochondrial entry point of gluconeogenesis. Key step: Pyruvate + CO2_2 + ATP →pyruvate carboxylase\xrightarrow{\textit{pyruvate carboxylase}} Oxaloacetate Which prediction is most consistent with increased pyruvate carboxylase activity in this context?
    Answer: Enhanced gluconeogenic capacity from pyruvate because oxaloacetate formation is increased This question tests allosteric activation of gluconeogenesis entry. Acetyl-CoA activates pyruvate carboxylase, enhancing oxaloacetate formation for gluconeogenesis. In these hepatocytes, high acetyl-CoA increases pyruvate carboxylase activity, supporting glucose production from pyruvate-derived substrates. Choice C is correct because it predicts enhanced gluconeogenic capacity via increased oxaloacetate. Choice B fails by suggesting inhibition, confusing acetyl-CoA's activator role. In similar questions, identify allosteric effectors from related pathways. Check if the activator signals substrate abundance for the pathway.
  15. In an isolated hepatocyte experiment, investigators compared metabolic flux during a fed-mimetic condition (high insulin, low glucagon) versus a fasting-mimetic condition (low insulin, high glucagon), keeping extracellular glucose constant. They observed that during the fed-mimetic state, cytosolic F2,6BP increased and net hepatic glucose output decreased. Based on the scenario, which metabolic shift would be expected in the liver during the fed-mimetic condition?
    Answer: Increased glycolysis via activation of PFK-1 and inhibition of fructose-1,6-bisphosphatase by F2,6BP This question tests understanding of F2,6BP's reciprocal regulation of glycolysis and gluconeogenesis. F2,6BP is a potent allosteric activator of PFK-1 (promoting glycolysis) and inhibitor of fructose-1,6-bisphosphatase (blocking gluconeogenesis). In the fed state with high insulin signaling, PFK-2/FBPase-2 is phosphorylated by protein kinase A in a way that activates its kinase activity, producing more F2,6BP. This simultaneously pushes carbon flow through glycolysis while preventing futile cycling through gluconeogenesis, explaining the decreased hepatic glucose output. Choice A incorrectly claims F2,6BP activates gluconeogenesis, while choice B wrongly states it inhibits glycolysis. Remember that F2,6BP acts as a metabolic switch: high levels favor glycolysis and storage, while low levels permit gluconeogenesis and glucose release.
  16. In an adipocyte culture model of oxidative stress, researchers increased NADP+^+ availability and observed a rapid rise in NADPH with unchanged lactate production. They concluded that flux was redirected into a pathway that generates reducing equivalents without directly producing ATP. Based on the scenario, which metabolic shift would be expected to be most consistent with increased oxidative PPP activity?
    Answer: Increased NADPH production with increased capacity for reductive biosynthesis and antioxidant defense This question tests understanding of the oxidative pentose phosphate pathway's function. The oxidative PPP, initiated by glucose-6-phosphate dehydrogenase, oxidizes glucose-6-phosphate while reducing NADP+ to NADPH. When NADP+ availability increases (the oxidized form), it drives the oxidative PPP forward, generating NADPH for reductive biosynthesis and antioxidant defense (via glutathione reductase). This pathway generates NADPH without producing ATP or lactate, explaining the unchanged lactate production. Choice B incorrectly claims the PPP produces ATP, while choice C wrongly states NADP+ inhibits the pathway. Remember that the oxidative PPP specifically generates NADPH (not ATP) and is driven forward by NADP+ availability as substrate for the dehydrogenase reactions.
  17. In primary hepatocytes, a selective inhibitor was added against fructose-1,6-bisphosphatase (FBPase-1) under gluconeogenic conditions (lactate as major carbon source; high glucagon signaling). Glucose release into the medium decreased within 30 min, while intracellular fructose-1,6-bisphosphate increased. Which prediction is most aligned with inhibition of fructose-1,6-bisphosphatase in this setting?
    Answer: Reduced gluconeogenic flux with accumulation of fructose-1,6-bisphosphate upstream of the inhibited step This question tests understanding of fructose-1,6-bisphosphatase's role in gluconeogenesis. FBPase-1 catalyzes a key regulatory step in gluconeogenesis, converting fructose-1,6-bisphosphate to fructose-6-phosphate. Inhibiting this enzyme blocks gluconeogenic flux at this step, causing accumulation of its substrate (fructose-1,6-bisphosphate) and preventing glucose synthesis from gluconeogenic precursors like lactate. This explains the decreased glucose release and increased intracellular fructose-1,6-bisphosphate observed. Choice B incorrectly suggests inhibition would increase flux, while choice D wrongly connects FBPase-1 to the PPP. Remember that enzyme inhibition causes substrate accumulation upstream and product depletion downstream of the blocked step.
  18. A liver-specific genetic variant increases the kinase activity of the bifunctional enzyme PFK-2/FBPase-2 while decreasing its phosphatase activity. In a fed state (high insulin, low glucagon), hepatocytes from these individuals show altered levels of fructose-2,6-bisphosphate (F2,6BP). Based on the scenario, which metabolic shift would be expected in the liver?
    Answer: Increased F2,6BP, increased PFK-1 activity, and decreased gluconeogenesis This question tests understanding of PFK-2/FBPase-2 bifunctional enzyme regulation of glycolysis and gluconeogenesis. This enzyme has kinase activity (producing fructose-2,6-bisphosphate) and phosphatase activity (degrading F2,6BP). The variant increases kinase activity while decreasing phosphatase activity, resulting in increased F2,6BP levels. F2,6BP is a potent allosteric activator of PFK-1 (glycolysis) and inhibitor of FBPase-1 (gluconeogenesis). In the fed state with high insulin, this would further enhance glycolysis through increased PFK-1 activity and suppress gluconeogenesis through FBPase-1 inhibition. This explains the metabolic shift in choice B. Choice A incorrectly predicts decreased F2,6BP, choice C wrongly states F2,6BP decreases PFK-1 activity, and choice D incorrectly limits F2,6BP regulation to the PPP. When analyzing bifunctional enzyme mutations, consider how the balance between opposing activities affects the regulatory metabolite concentration.
  19. A cell-free cytosolic extract from human erythrocytes was supplied with glucose-6-phosphate (G6P) as the only carbon input. Under condition 1, NADP+^+ was abundant; under condition 2, NADPH was added to raise the NADPH/NADP+^+ ratio while keeping total NADP(H) constant. All other substrates and cofactors were unchanged. The investigators monitored CO2_2 release from the oxidative branch of the pentose phosphate pathway (PPP) over 5 minutes. Based on the scenario, which metabolic shift would be expected when the NADPH/NADP+^+ ratio is increased?
    Answer: Decreased oxidative PPP flux because glucose-6-phosphate dehydrogenase is inhibited by NADPH This question tests understanding of feedback inhibition in the oxidative pentose phosphate pathway (PPP). Glucose-6-phosphate dehydrogenase (G6PD) catalyzes the rate-limiting step of the oxidative PPP, converting G6P to 6-phosphoglucono-δ-lactone while reducing NADP+ to NADPH. G6PD is strongly inhibited by its product NADPH through negative feedback regulation. When the NADPH/NADP+ ratio is increased (condition 2), G6PD activity decreases, reducing flux through the oxidative PPP and thus decreasing CO2 release from the decarboxylation steps. This regulatory mechanism ensures NADPH production matches cellular needs. Choice A incorrectly states NADPH activates G6PD, choice C wrongly claims the PPP generates ATP, and choice D incorrectly places the oxidative PPP in mitochondria when it occurs in the cytosol. To identify similar regulatory patterns, look for product inhibition of rate-limiting enzymes in biosynthetic pathways.
  20. A pharmacology report (150–250 words) described a compound that increases intracellular fructose-2,6-bisphosphate (F2,6BP) in cardiomyocytes without changing oxygen availability. Upon treatment, cells showed increased glucose consumption and increased lactate release, with no change in NADPH. The authors suggested enhanced glycolysis at a key regulatory step. Regulatory context: F2,6BP strongly activates PFK-1 Which outcome is most consistent with increased F2,6BP in cardiomyocytes?
    Answer: Increased glycolytic flux through PFK-1, increasing pyruvate formation and lactate under high demand This question tests F2,6BP's activation of cardiac glycolysis. F2,6BP potently activates PFK-1, increasing glycolytic flux and lactate production in high-demand tissues. In these cardiomyocytes, compound-induced F2,6BP enhances glucose consumption and lactate release via PFK-1. Choice D is correct because it links F2,6BP to increased PFK-1 flux and pyruvate/lactate formation. Choice B fails by stating F2,6BP inhibits PFK-1, reversing its activator role. For similar questions, recall tissue-specific regulators of glycolysis. Verify if the outcome supports energy demand without PPP involvement.

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