Neuropeptides, now recognized to be vitally involved in many central and peripheral functions, are known to be generated from larger precursors via a variety of postranslational modifications. In particular, carboxyl terminus alpha-amidation is a key structural feature in the biological activity (and probably in regulation and resistance toward C-exopeptidases) of many neurohormones, with ca. 50% of known peptide hormones being amidated at their C-terminii. Although both the enzymology and biochemistry of amidation have been under active investigation for some time, only within the last two years has it become clear that amidation is actually a two step process. The enzyme peptidylglycine alpha-amidating monooxygenase (PAM) catalyzes formation of the alpha-hydroxyglycine derivative of the glycine extended substrate. Our laboratory recently isolated a novel enzyme from neurointermediate pituitary which we have named peptidylamidoglycolate lyase (PGL; see attached letter documenting consent of the Chairman of the Enzyme Nomenclature Commission of the IUB to this name). We demonstrated that PGL catalyzes the second step in neuropeptide amidation -- dealkylation of alpha-hydroxyglycine derivatives to produce the final amide product. In addition, our laboratory has also demonstrated the presence of both PAM and PGL in chromaffin granules, and we have developed the first small molecule substrates as well as new sensitive assays for the enzymes. In view of the emerging recognition of the crucial neurochemical role of alpha-amidation, we propose to initiate a new research program focusing on this process. Our goals are to explore the regulation of neuropeptide amidation and its relationship to catecholamine processing in chromaffin cells, to characterize amidating enzymes from various sources, and to design and characterize novel classes of inhibitors and mechanism-based effectors for neuropeptide amidation.
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