Abstract
A secretory granule-associated enzymatic activity that converts mono-[125I]-D-Tyr-Val-Gly into mono-[125I]-D-Tyr-Val-NH2 has been studied. The activity is primarily soluble and shows optimal activity at pH 7 to pH 8. Amidation activity was stimulated 9-fold by addition of optimal amounts of copper (3 μM). In the presence of optimal copper, ascorbate stimulated the reaction 7-fold; none of the other reduced or oxidized cofactors tested was as effective. Taking into account the dependence of the reaction on ascorbate and molecular oxygen and the production of glyoxylate [2], it is suggested that the α-amidation enzyme is a monooxygenase. Lineweaver Burk plots with D-Tyr-Val-Gly as the varied substrate demonstrated Michelis-Menten type kinetics with the values of Km and Vmax increasing with the addition of ascorbate to the assay. A variety of peptides ending with a COOH-terminal Gly residue act as inhibitors of the reaction. Two synthetic peptides, γ2MSH and ACTH(1-14), with carboxyl termini similar to the presumed physiological substrates for the enzyme, act as competitive inhibitors with similar K1 values. It is likely that this secretory granule α-amidation activity is involved in the physiological biosynthetic α-amidation of a wide range of bioactive peptides.
Original language | English (US) |
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Pages (from-to) | 921-928 |
Number of pages | 8 |
Journal | Peptides |
Volume | 4 |
Issue number | 6 |
DOIs | |
State | Published - 1983 |
Externally published | Yes |
Keywords
- Ascorbate
- Bovine intermediate pituitary
- Copper
- Molecular oxygen
- Peptide α-amidation
- αMSH
- γMSH
ASJC Scopus subject areas
- Biochemistry
- Physiology
- Endocrinology
- Cellular and Molecular Neuroscience