Certain kinds of bacteria, known as thermophilic bacteria, have adapted to be able to live in hot springs. Because of the very hot temperatures they live in (55°C, compared to a normal mammalian body...

Certain kinds of bacteria, known as thermophilic bacteria, have adapted to be able to live in hot springs. Because of the very hot temperatures they live in (55°C, compared to a normal mammalian body temperature of 38°C), thermophilic bacteria must have made adaptations in their proteins, particularly the enzymes that catalyze the biochemical reactions the bacteria need to obtain energy. Thermophilic bacteria share with other closely related bacteria (and most other cells) an important enzyme called malate dehydrogenase (MDH). There is some evidence that the thermophilic bacterium Chloroflexus aurantiacus diverged early in its evolution from many other thermophilic bacteria. To explore this further, Rolstad and coworkers † wanted to characterize the MDH of this bacterium. One of the features they wanted to determine was the optimum pH for the function of this enzyme. They measured enzyme activity A in terms of the reduction of the substrate oxalacetate expressed as a percentage of rate under standard conditions at pH = 7.5. Using buffers, the pH was varied over the range of 4.3–8.3 (the data are in Table D-16, Appendix D). Is there evidence of an optimum pH in this range? If so, discuss the strength of the evidence.

Table D-16