Production and Regulation of Levels of Amidated Peptide Hormones

Abstract

Peptide hormones with a C-terminal amide regulate numerous physiological processes and are associated with many disease states. Consequently, the key enzymes involved in their production, peptidylglycine α-amidating monooxygenase and carboxypeptidase E, have been studied intensively. This review surveys what is known about the enzymes themselves and their cofactors, as well as their substrates and competitive and mechanism-based inhibitors.

Inactivation of peptidylglycineα-hydroxylating monooxygenase by cinnamic acid analogs

“…We find that inactivated PHM is indistinguishable from untreated enzyme and find no evidence for cinnamate oxidation during the inactivation reaction. The reversible Michael addition of an active site nucleophile to cinnamate could account for our data and may explain the inactivation of PHM by a variety of acrylates 20,30,35 , and the 2- and 3-alkenoates 32 as well as provide an explanation for the lack of PHM-labeling by 3 H-PBA 37 .…”

“…Like the chemistry proposed for the olefinic inactivation of DβM and P 450 , it has been suggested that olefinic inactivation of PHM results from the formation of a non-epoxide oxidized species, likely an olefin-derived radical 25,33,35–38,64 . This hypothesis is reasonable given that inactivation is turnover-dependent and that the PHM-catalyzed hydroxylation reaction likely proceeds through a substrate-based radical 39–42 .…”

“…We propose that the PBA-mediated inactivation of PHM occurs by more than one process. Inactivation by PBA could occur via Michael addition/Cu(I) chelation, like the chemistry we have outlined above, and via a reaction between an active site amino acid and PBA-derived radical 35–37 . PHM inactivation by a PBA-derived radical would lead, most likely, to a covalent bond between PBA and the enzyme.…”

“…Intriguingly, Bradbury et al 33 suggest that cinnamate-mediated inactivation of PHM results from the formation of a vinyl radical (Figure 1). This chemistry is related to the irreversible inactivation of PHM by trans -benzoylacrylate 25 , trans -4-phenyl-3-butenoate (PBA, also known as trans -styrylacetate) 36,37 , and trans -styrylthioacetate 38 ; PBA inactivation is proposed to occur via the formation of an allylic radical (Figure 1) 35,37 . The formation of vinyl radical during the cinnamate-mediated inactivation of PHM is mechanistically relevant because this would require the formation of a PAM-based oxidant that is sufficiently strong to abstract a hydrogen atom from the α-carbon of cinnamate.…”

Beckwith Memorial Symposium on Free Radical Chemistry

“…In 'Computational Evaluation of the Sulfonyl Radical as a Universal Leaving Group for RAFT Polymerisation', M. L. Coote et al [11] report an application of free radical chemistry to advance polymer science; M. A. Terzidis and C. Chatgilialoglu [12] use radicals in chemical synthesis in 'Radical Cascade Protocol for the Synthesis of (5 0 S)-and (5 0 R)-5 0 ,8-Cyclo-2 0 -deoxyguanosine Derivatives'; J. A. Murphy and co-workers [13] explore radicals as organic reducing agents in 'A Novel Organic Electron Donor Derived from N-Methylisatin'; and F. Cao and C. J. Easton [14] review the 'Production and Regulation of Levels of Amidated Peptide Hormones', fundamental physiological processes where free radicals are intimately involved.…”