AJP - Endocrinology and Metabolism, Vol 252, Issue 3 E320-E326, Copyright © 1987 by American Physiological Society
Effects of D-amino acid substituents on degradation of LHRH analogues by proximal tubule
G. Flouret, T. Majewski, D. R. Peterson, A. J. Kenny and F. A. Carone
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.
