Lactate Dehydrogenase Activity in Dog Adipose Tissue. ∗

Abstract

Summary

Within the same animal, LDH activity is significantly higher in the peri-cardial than in the inguinal adipose tssue. This is related to the flavoprotein content of the two tissues. High pyruvate concentrations inhibit LDH activity from either source to the same extent. The degree of inhibition by urea is always significantly less (p<.005) at the high (1 × 10⁻² M) than at the low (5 × 10⁻⁴ M) pyruvate level. Oxalate inhibits inguinal adipose tissue LDH less at the high than at the low pyruvate level, while showing a reverse effect on the enzyme from peri-cardial tissue. Michaelis-Menten constants (K_M) for pyruvate were calculated from activities both in the absence and in the presence of urea and oxalate. K_M values were significantly decreased in the presence of 2.0 M urea. All levels of oxalate studied increased the K_M of pericardial adipose tissue LDH, but did not affect that of the inguinal adipose tissue enzyme. Incubation at 59°C for 10 minutes inactivates both enzymes to about the same extent, leading to a loss of 44 and 47% of their activity, respectively. Electrophoretic separation revealed 5 isozymes with a higher proportion of fast moving subunits in pericardial adipose tissue LDH.