Adaptation of muscle pyruvate kinases to environmental temperatures and pressures

Kinetic and structural properties of muscle pyruvate kinases from species adapted to different temperatures and hydrostatic pressures were examined. Most muscle pyruvate kinases can exist in two temperature-dependent conformational states. For the low temperature conformers, activation free energies and enthalpies were proportional to the species' adaptation temperatures. The interspecific differences in activation parameters may be due to different amounts of weak bond formation/rupture during the rate-limiting event(s) in catalysis. When comparisons of substrate binding ability at physiological temperatures are made, a marked conservation in apparent Km values is observed among species, Structural rigidity, as estimated by heat inactivation temperature, is positively correlated with adaptation temperature. The apparent size of the conformational change which occurs during catalysis is also positively correlated with cell temperature, except for enzymes for deep-sea species.