Enhanced activity of brain lipase in the presence of adrenocorticotrophic hormone. Comparison with a colipase effect.
The characteristics of the pH-dependent stimulatory influence of adrenocorticotrophic hormone (ACTH) on lipolysis (Arnaud, J., Nobili, O. and Boyer, J. (1980) Biochim, Biophys. Acta 617, 524-528) were investigated further. ACTH enhanced 7-30 times the rates of hydrolysis of emulsified trioleoylglycerol by a rat brain lipase, when added to the medium both before and after the enzyme. When lipase activity was inhibited by sodium taurocholate, ACTH fully reversed the inhibition at bile salt concentration up to 2 mM. The reactivation process followed a sharp S-shaped pattern, leveling off at about 10(-4) M ACTH. With and without bile salt, the stimulatory effect of ACTH culminated at pH 5.75, and was dependent on the presence of trace amount of a water-insoluble solvent in the substrate emulsion. Taken together, the results suggest that ACTH acts at the lipid-water interface in facilitating the enzyme-substrate interaction. The relevance of the hormonal influence to a colipase-like effect is discussed.
D000324:Adrenocorticotropic Hormone / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000201:enzymology*; D003089:Colipases / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D006586:Hexanes / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008049:Lipase / Q000378:metabolism*; D008297:Male; D009994:Osmolar Concentration; D011506:Proteins / Q000494:pharmacology*; D051381:Rats; D013656:Taurocholic Acid / Q000494:pharmacology
D003089:Colipases; D006586:Hexanes; D011506:Proteins; D013656:Taurocholic Acid; D000324:Adrenocorticotropic Hormone; D008049:Lipase