No abstract

No abstract

Mh MI 1 I 3 0 C 40 C Tern perature u -LDH-51 J i t LDH-1 4 C LDH-1 h I L @ 25c 30 C Temperature 40 C FIG. 1. Effect of temperature on LDH activity. M = breast muscle, H = heart muscle. I = 3.3 X M pyruvate, h = 6.6 X lo-' M pyruvate. One unit of LDH equals the amount of enzyme utilizing 1 pmole of NADH per minute. FIG. 2. Effect of temperature on LDH 1 and LDH 5 a t high and low pyruvate concentration. The individual isozymes were obtained by elution from starch gel after electrophoresis of heart and muscle supernatants for 16 hr at 4°C. h = 6.6 X lo-' M pyruvate, 1 = 3.3 X M pyruvate. muscle homogenate, and isolated breast muscle LDH 5 both have greater activity at high pyruvate concentration than at low, especially at the physiological body temperature of the chicken (40OC). The LDH in the supernatant of a chicken heart muscle homogenate, and isolated LDH 1 react best at low pyruvate concentration, the difference, however, is less marked at 40OC. These data are in accord with the observation of Cahn et aE ( 3 ) on the differential sensitivity of LDH 1 and LDH 5 to pyruvate concentration.Summary. Spectrophotometric analysis of chick lactate dehydrogenase activity showed that the LDH in breast muscle supernatant and isolated LDH 5 had greater activity at high pyruvate concentration than at low. The difference was more marked at 40°C than at lower temperatures. Heart muscle LDH, and isolated LDH 1 reacted best at low pyruvate concentration. The difference was less marked at 40°C than at lower temperatures.