Effects of D-amino acid substituents on degradation of LHRH analogues by proximal tubule.
Less than Glu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2, the luteinizing hormone-releasing hormone, LHRH, is degraded in renal proximal tubules (PT) in vivo (rat) and in vitro (rabbit) to less than Glu-His (2), less than Glu-His-Trp (3), and less than Glu-His-Trp-Ser (4). LHRH may be cleaved by endopeptidases simultaneously at multiple bonds, or initially at Ser4-Tyr5 followed by carboxypeptidase hydrolysis of 4 to 3 and then 2. To distinguish between these mechanisms, [3H]LHRH analogues were incubated with rabbit renal brush-border membranes (BBM), microinfused into PT in vivo or in vitro, and products were analyzed by HPLC. [D-Ser4]LHRH was not cleaved at D Ser4-Tyr5 but yielded less than Glu-His-Trp-D-Ser-Tyr-Gly as the major metabolite plus 2 and 3. [D-Trp6]LHRH was cleaved by BBM and PT to 2 and 3, but not to 4. [D-Ser4, D-Trp6]LHRH was not cleaved by BBM, but was degraded to 2 by PT in vivo. Thus, D-amino acid substituents altered the expected cleavage pattern of these analogues. [3H]LHRH was cleaved by BBM or by endopeptidase-24.11 from porcine PT to metabolites 2, 4, small amounts of 3, and less than Glu-His-Trp-Ser-Tyr-Gly, but cleavage was strongly inhibited by the specific inhibitor phosphoramidon. Thus, normally LHRH may be cleaved in PT by endopeptidase-24.11 to 2 and 4, and by angiotensin I-converting enzyme to 3, its known cleavage site.
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D010450:Endopeptidases / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D006728:Hormones / Q000378:metabolism; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008871:Microvilli / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
D000596:Amino Acids; D006728:Hormones; D007987:Gonadotropin-Releasing Hormone; D010450:Endopeptidases