Phospholipid requirement of epididymal testosterone 5α-reductase and phospholipid composition of epididymal microsomes

Abstract

We have investigated phospholipid requirement for testosterone 5α-reductase solubilized from microsomal and nuclear fractions of rat epididymis. The 5α-reductase from microsomal fraction was stimulated by phosphatidylcholine (PC) with long acyl-chain lengths, but inhibited by short chain PC. The nuclear enzyme activity was weakly activated by PC with various acyl-chain lengths tested. Synthetic phosphatidylserine (PS), such as dioleoylPS, most strongly stimulated the microsomal enzyme activity, but did not exhibit any activation of the nuclear enzyme activity. Endogenous phospholipids, such as PC, PS, and phosphatidylethanolamine (PE) separated from bovine epididymal microsomes were tested for their stimulatory effects on microsomal and nuclear enzymes. Among these endogenous phospholipids, PS most greatly stimulated the microsomal 5α-reductase activity, whereas both PC and PE weakly activated the enzyme activity. On the other hand, endogenous PC and PS had no ability to support the nuclear enzyme activity. The fatty acid compositions of PC and PS from bovine epididymal microsomes were determined, in order to elucidate the relationship between 5α-reductase activation by these phospholipids and the structure of their acyl chains. The relative content of fatty acids in PC, in a decreasing order, was palmitate linolate > oleate; that in PS was stearate > oleate > palmitate. Based on these observations, the roles of microsomal PS and PC in epididymal 5α-reductase reaction will be discussed.