Delta 5-3 beta-hydroxysteroid acyl transferase activity in the rat brain.
Pregnenolone and dehydroepiandrosterone accumulate in brain as sulfate and fatty acid esters and unconjugated steroids. The steroid fatty acid ester-synthesizing activity was investigated in rat brain microsomes. Endogenous fatty acids in the microsomal fraction were used for the esterification of steroids. The enzyme system had a pH optimum of 4.5 in acetate buffer with [3H]dehydroepiandrosterone as substrate. The apparent Km was 9.2 +/- 3.1 x 10(-5) M and Vmax was 18.6 +/- 3.4 nmol/h/mg protein (mean +/- SEM). The inhibition constants of pregnenolone and testosterone were 123 and 64 microM, respectively. Results were compatible with a competitive type of inhibition. A high level of synthetic activity was found in the brain of 1- to 3-week-old male rats, which rapidly decreased with aging. Saponification of purified [3H]pregnenolone esters yielded pregnenolone and a mixture of palmitate, oleate, linoleate, stearate, and myristate as the predominant fatty acids. Contrasting with the high rates of esterification of several radioactive delta 5-3 beta-hydroxysteroids or 17 beta-hydroxysteroids, no fatty acid esters of either cholesterol, epitestosterone (with a hydroxyl group at position C-17 alpha), or corticosterone (with hydroxyl groups at C-21 and C-11 beta) were formed in the same incubation conditions.
Vourc'h
C
C
Unité 33, INSERM, Hôpital de Bicêtre, France.
Eychenne
B
B
Jo
D H
DH
Raulin
J
J
Lapous
D
D
Baulieu
E E
EE
Robel
P
P
D000217:Acyltransferases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000375:Aging / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000201:enzymology* / Q000254:growth & development; D003687:Dehydroepiandrosterone / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008297:Male; D008861:Microsomes / Q000201:enzymology; D011284:Pregnenolone / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013379:Substrate Specificity; D013739:Testosterone / Q000494:pharmacology
D005227:Fatty Acids; D013739:Testosterone; D003687:Dehydroepiandrosterone; D011284:Pregnenolone; D000217:Acyltransferases; C076790:delta5-3beta-hydroxysteroid acyltransferase