Long-chain acyl-CoA synthetase of rat testis microsomes. Substrate specificity and hormonal regulation.
We investigated long-chain fatty-acyl-CoA synthetase activity in rat testicular microsomes. The apparent Michaelis constants (Km's) for the substrate fatty acids increased while their corresponding maximal velocities decreased in the order 18:3(n-3), 20:3(n-6), and 18:0. The reaction with 20:3 as substrate was diminished in the presence of a constant amount of either 18:0, 18:2(n-6), or 18:3(n-3) in a manner consistent with their action as simple competitive inhibitors, with the Ki values for 18:0 and 18:3(n-3) being of the same order of magnitude as their respective Km's. Adrenocorticotrophin and/or dexamethasone administration to intact rats caused a significant decrease in the thioesterification of all three substrates without producing any alteration in the fatty-acid composition of the microsomal membranes. These results indicate the presence of a broad-specificity activating enzyme in testis whose function is subject to hormonal regulation.
Hurtado de Catalfo
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GE
Instituto de Investigaciones Bioquímicas de La Plata (INIBIOLP), Facultad de Ciencias Médicas, La Plata, Argentina.
de Gómez Dumm
I N
IN
Mandon
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EC
D000818:Animals; D003066:Coenzyme A Ligases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005227:Fatty Acids / Q000096:biosynthesis; D006728:Hormones / Q000502:physiology; D008297:Male; D008861:Microsomes / Q000201:enzymology*; D051381:Rats; D017208:Rats, Wistar; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D013379:Substrate Specificity; D013737:Testis / Q000201:enzymology* / Q000648:ultrastructure; D000098859:Long-Chain-Fatty-Acid-CoA Ligase
D005227:Fatty Acids; D006728:Hormones; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D003066:Coenzyme A Ligases; C090799:FAA2 protein, S cerevisiae; D000098859:Long-Chain-Fatty-Acid-CoA Ligase