LDH activity and isozyme patterns in crayfish (Orconectes nais) under conditions of seasonal change.

Abstract

In the crayfish Orconectes nais, LDH is present in two isozymatic forms. Isozymes from gill, abdominal muscle, heart and nerve have the same mobility indicating that they possess the same polypeptide composition. However, isozymes from hepatopancreas and intestine moving more cathodically suggests these isozymes are more positively charged. Isozyme patterns did not differ under different seasons suggesting no seasonal changes in the LDH isozyme composition of each tissue. The relative activities of the isozymes demonstrate that LDHs from gill, abdominal muscle, heart, and nerve are all M-type. These M-type LDHs with a ratio (0.33 mM pyruvate substrate/10 mM pyruvate substrate) close to 0.5 show that activity increases with an increase in pyruvate concentration. This is different from that of rat skeletal muscle which has a ratio of 1.67 indicating isozyme inhibition with high pyruvate concentrations. The effect of protease inhibitors on LDH activities from hepatopancreas and intestine suggests that hepatopancreas has relatively low LDH activity. Gill, abdominal muscle, heart, -and nerve show seasonality in the level of LDH activity. The physiological significance of the seasonality in LDH activity for seasonal adaptation is discussed. Key words: Lactate dehydrogenase; LDH; Orconectes nais.