PHOSPHOLIPID REQUIREMENT OF EPIDIDYMAL TESTOSTERONE 5-ALPHA-REDUCTASEAND PHOSPHOLIPID-COMPOSITION OF EPIDIDYMAL MICROSOMES

We have investigated phospholipid requirement for testosterone 5alpha- reductase solubilized from microsomal and nuclear fractions of rat epi didymis. The 5alpha-reductase from microsomal fraction was stimulated by phosphatidylcholine (PC) with long acyl-chain lengths, but inhibite d by short chain PC. The nuclear enzyme activity was weakly activated by PC with various acyl-chain lengths tested. Synthetic phosphatidylse rine (PS), such as dioleovlPS, most strongly stimulated the microsomal enzyme activity, but did not exhibit any activation of the nuclear en zyme activity. Endogenous phospholipids, such as PC, PS, and phosphati dylethanolamine (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 5alpha-reductase activity, whereas both PC and PE weakly a ctivated 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 deter mined, in order to elucidate the relationship between 5alpha-reductase activation by these phospholipids and the structure of their acyl cha ins. 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 an d PC in epididymal 5alpha-reductase reaction will be discussed.