An Initial Reaction Rate Assay for "Glycerate Dehydrogenase"

Abstract Concentrations of substrate, coenzyme, and hydrogen ion, optimal for the reduction of hydroxypyruvate at 37°C by normal and pathological human sera are described. We confirmed, by using the supernatant fluid from homogenized human heart and liver tissue, that the faster-moving isoenzymes have a greater affinity for substrate and coenzyme than the slowermoving isoenzymes, which require higher concentrations for saturation. LDHx, present in human seminal plasma, appears to have the lowest Michaelis constant for hydroxypyruvate. Glycerate dehydrogenase was found to be stable if the standard assay temperature was increased from 25° to 37°C.