Enolase is an enzyme that catalyzes one reaction in glycolysis in all organisms that carry out this process. The amino acid sequence of enolase is similar but not identical in the organisms. Researchers purified enolase from Saccharomyces cerevisiae, a single-celled eukaryotic yeast that grows best at 37°C , and from Chloroflexus aurantiacus, a bacterium that grows best at the much higher temperature of 55°C . The researchers compared the activity of purified enolase from the two organisms by measuring the rate of the reaction in the presence of varying concentrations of substrate and a constant amount of each enzyme at both 37°C and 55°C .

(a) Depending on the organism, the optimal pH for enolase to catalyze its reaction is between 6.5 and 8.0 . Describe how a pH below or above this range is likely to affect enolase and its catalytic ability.

(b) Identify the appropriate negative control the researchers most likely used when measuring the reaction rate in the presence of each organism’s enolase.

(c) The researchers predict that for any particular concentration of substrate, the C. aurantiacus enolase-catalyzed reaction is more rapid at 55°C than at 37°C . Provide reasoning to justify the researchers’ prediction.