Enzyme Structure and Catalysis (5E) Practice Test

A competitive inhibitor I has $K_i=5\ \mu$M for an enzyme with $K_m=10\ \mu$M. In an assay with I = 5 \muM, $V_{max}$ is unchanged. Which statement is most consistent with the observed kinetics?

An enzyme involved in intestinal carbohydrate digestion uses two active-site residues: Asp (general acid) and His (general base). Site-directed mutagenesis replaces Asp with Asn (D→N) without altering overall folding (confirmed by circular dichroism). At pH 7.0, the mutant shows unchanged substrate binding affinity but a 100-fold decrease in $k_{cat}$. Which statement best explains the catalytic mechanism of the enzyme?