Proteolysis of adrenocorticotropin in brain. Characterization of cleavage sites by peptidases in synaptic membranes and formation of peptide fragments.
The biotransformation of adrenocorticotropin (ACTH-(1-39)) by brain synaptic membranes has been studied. Peptide fragments of ACTH-(1-39) which were formed during in vitro incubation of the peptide with membrane preparations were isolated by high pressure liquid chromatography and characterized by determination of amino acid composition and NH2- terminal residue. At pH 7.4, ACTH-(1-38) was found as the main metabolite, together with ACTH-(7-21) and ACTH-(7-20). In addition, a series of secondary products was identified. At pH 6.2, ACTH-(1-38), ACTH-(1-37), and ACTH-(1-36) were exclusively formed, while at pH 8.5, ACTH-(1-39) was converted into ACTH-(1-16), ACTH-(17-39), ACTH-(22-39), and ACTH-(3-15). Time course experiments demonstrated the action of a carboxypeptidase activity and a trypsin-like endopeptidase on ACTH-(1-39) as predominant proteolytic events. The carboxypeptidase was optimally active at pH values of 5.7 or below. These enzymes play an essential role in the stepwise conversion of ACTH-(1-39) in brain. It is suggested that they are involved in the modulation of the central activities of ACTH fragments in the brain.
D000324:Adrenocorticotropic Hormone / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001711:Biotransformation; D001921:Brain / Q000201:enzymology*; D002851:Chromatography, High Pressure Liquid; D007700:Kinetics; D008297:Male; D010447:Peptide Hydrolases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013379:Substrate Specificity; D013552:Swine; D013570:Synaptic Membranes / Q000201:enzymology*
D000324:Adrenocorticotropic Hormone; D010447:Peptide Hydrolases