ALDRIN EPOXIDASE ACTIVITY OF RAT LIVER AND RAT LIVER MICROSOMES UNDER VARIOUS CONDITIONS OF STORAGE

The stability of rat hepatic microsomal mixed function oxidation systems stored under various conditions was assessed by a measurement of aldrin epoxidase, NADPH cytochrome c reductase, NADPH neotetrazolium reductase activities and cytochrome P-450 levels. Male rat livers stored at - 20° for 30 days showed little loss of the two NADPH-dependent microsomal reductase activities and cytochrome P-450. Microsomal suspensions from these livers showed higher protein content, increased aldrin epoxidase activity, decreased endogenous as well as NADPH-dependent lipid peroxidation and higher stability during storage at 4°. The microsomal epoxidase systems of liver were less stable when stored as microsomal pellets than as whole liver at either -10° or-20°. Enzymes in microsomal suspensions prepared from fresh liver were unstable at 4°, but retained full activity if the suspensions contained 10-2 M KCN or were prepared from prefrozen livers. These results indicate that freezing of the liver causes a structural change in microsomes resulting in an increase in epoxidase activity. © 1969.