Purification and comparison of liver microsomal flavin-containing monooxygenase from normal and streptozotocin-diabetic rats.

Liver microsomal flavin-containing monooxygenase (FMO) activity towards thiobenzamide is two-fold increased in streptozotocin diabetic (insulin deficient) rats and mice and, to a lesser degree in congenital insulin resistant Ob/Ob mice. No difference in thermal stability appears between microsomal FMOs from both normal and diabetic rats. FMO has been purified to homogeneity from these two sources, with a 50-fold increase of specific activity. Their apparent molecular weight is respectively 50,000 and 49,000 and a discrete modification appears in the HPLC profiles of tryptic peptides from purified FMOs. They appear immunochemically very similar and present in equal quantity in microsomal membranes from both normal and diabetic rats, so that the increased activity cannot be ascribed to an increased concentration of the enzyme protein.