Effects of Hydrostatic Pressure on Catalysis by Different Lactate Dehydrogenase Isozymes from Tissues of an Abyssal Fish

SYNOPSIS. The predominant lactate dehydrogenases (LDH's) occurringin liver, heart, and muscle of a benthic Coryphaenoides speciesare electrophoretically distinguishable from each other. Maximumrates of pyruvate reduction catalyzed by heart and muscle LDH'sshow an optimum pH near neutrality, while liver LDH activitydisplays an unusual alkaline pH optimum. Pyruvate saturationcurves are Michaelis-Menten in form for all three preparations.Maximum catalytic rates and the apparent K_m (pyruvate) are pressureindependent for liver and heart LDH's. In the case of muscleLDH's, the maximum catalytic rate is also pressure insensitive,but the K_m is dramatically increased by pressure. These experimentsdearly indicate that, at low substrate concentrations, the preciseeffects of pressure on enzyme-catalyzed reactions depend uponthe nature and origin of the catalyst.