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Endopeptidase‐24.15 Is the Primary Enzyme that Degrades Luteinizing Hormone Releasing Hormone Both In Vitro and In Vivo
Author(s) -
Molineaux Christopher J.,
Lasdun Abraham,
Michaud Charlene,
Orlowski Marian
Publication year - 1988
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1988.tb01084.x
Subject(s) - endopeptidase , anterior pituitary , medicine , endocrinology , enzyme , in vivo , peptide hormone , chemistry , hypothalamus , luteinizing hormone , in vitro , hormone , enzyme inhibitor , pituitary gland , thyrotropin releasing hormone , biochemistry , biology , microbiology and biotechnology
The concentration of luteinizing hormone releasing hormone (LHRH) (pGlu‐His‐Trp‐Ser‐Tyr‐Gly‐Leu‐Arg‐Pro‐Gly‐NH 2 ), which reaches the anterior pituitary via the hypothalamo‐hypophyseal portal system, appears to be controlled in part by the rate of LHRH degradation within the hypothalamus and/or pituitary. Specific, active site‐directed endopeptidase inhibitors synthesized in our laboratory were used to identify the enzyme(s) involved in LHRH degradation by hypothalamic and pituitary membrane preparations, and by an intact anterior pituitary tumor cell line (AtT20). Incubation of LHRH with pituitary and hypothalamic membrane preparations led to the formation of pGlu‐His‐Trp (LHRH 1–3 ) as the main reaction product. Under the same conditions, addition to the incubation mixtures of captopril, an inhibitor of the angiotensin converting enzyme, led to accumulation of pGlu‐His‐Trp‐Ser‐Tyr (LHRH 1–5 ) and, to a lesser extent, pGlu‐His‐Trp‐Ser‐Tyr‐Gly (LHRH 1–6 ). The degradation of LHRH and the formation of the N‐terminal tri‐ and pentapeptides was blocked by N ‐[1‐( R,S )‐carboxy‐3‐phenylpropyl]‐Ala‐AlaPhe‐ p ‐aminobenzoate (cFP‐AAF‐pAB), a specific, active site directed inhibitor of endopeptidase‐24.15. Some inhibition of LHRH degradation and formation of the N‐terminal hexapeptide was also obtained in the presence of N‐[ 1‐carboxy‐2‐phenylethyl]‐Phe‐ p ‐aminobenzoate (cFE‐F‐pAB), an inhibitor of endopeptidase‐24.11. Similar results were obtained with AtT20 cell membranes and with intact AtT20 cells in monolayer culture. Following cleavage by endopeptidases the C‐terminal part of LHRH was rapidly degraded by aminopeptidases. Superactive analogs of LHRH in which Gly 6 was replaced by a D‐amino acid are resistant to degradation by both endopeptidase‐24.11 and ‐24.15. In vivo, when LHRH was injected directly into the third ventricle of rats, the presence of cFP‐AAF‐pAB inhibited LHRH degradation. It is concluded that LHRH degradation is primarily initiated by the membrane‐bound form of endopeptidase‐24.15 to yield pGlu‐His‐Trp‐Ser‐Tyr and to a lesser extent by endopeptidase‐24.11 to yield pGlu‐His‐Trp‐Ser‐Tyr‐Gly.