Temperature dependency of 5′-nucleotidase and acid phosphatase in muscle microsomes of fish

Relationships between kinetics of IMP dephosphorylation by muscle microsomal enzymes and lipid composition of muscle microsomes were compared among fish of different habitat temperature, yellowtail grunt, Spanish mackerel, rainbow trout and Pacific cod. The Km values of microsomal 5'-nucleotidase of fish except cod markedly increased at a temperature range below the break point on the Arrhenius plots of the enzyme activity. The break point temperatures in Arrhenius plots for microsomal 5'-nucleotidase were correlated with the content of saturated and polyunsaturated fatty acids in phospholipids of muscle microsomes in the fish examined. The results suggest that the occurrence of a break point in the Arrhenius plot of microsomal 5'-nucleotidase may be caused by the lipid phase transition of membranes that bind 5'-nucleotidase. Break point temperature may depend on microsomal lipid composition which is closely related to the habitat temperature of the fish. (C) 1998 Elsevier Science Inc.