TEMPERATURE DEPENDENCY OF 5'-NUCLEOTIDASE AND ACID-PHOSPHATASE IN MUSCLE MICROSOMES OF FISH

Relationships between kinetics of IMP dephosphorylation by muscle micr osomal enzymes and lipid composition of muscle microsomes were compare d among fish of different habitat temperature, yellowtail grunt, Spani sh mackerel, rainbow trout and Pacific cod. The Km values of microsoma l 5'-nucleotidase of fish except cod markedly increased at a temperatu re range below the break point on the Arrhenius plots of the enzyme ac tivity. The break point temperatures in Arrhenius plots for microsomal 5'-nucleotidase were correlated with the content of saturated and pol yunsaturated fatty acids in phospholipids of muscle microsomes in the fish examined. The results suggest that the occurrence of a break poin t in the Arrhenius plot of microsomal 5'-nucleotidase may be caused by the lipid phase transition of membranes that bind 5'-nucleotidase. Br eak point temperature may depend on microsomal lipid composition which is closely related to the habitat temperature of the fish. (C) 1998 E lsevier Science Inc.