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Protein Science, Vol 7, Issue 12 2684-2687, Copyright © 1998 by Cold Spring Harbor Laboratory Press
ACCELERATED COMMUNICATION |
K. W. WALKER and R. A. BRADSHAW
Department of Physiology and Biophysics, College of Medicine, University of California, Irvine, California 92697
Yeast methionine aminopeptidase I (MetAP I) is one of two enzymes in Saccharomyces cerevisiae that is responsible for cotranslational cleavage of initiator methionines. It has previously been classified as a Co(2+) metalloprotease in all prokaryotic and eukaryotic forms studied. However, treatment of recombinant apo-MetAP I with 12.5 {mu}M Zn(2+) produces an enzyme that is as active as that reconstituted with 200 {mu}M Co(2+). In the presence of physiological concentrations of reduced glutathione (GSH), Co-MetAP I is inactive, while the activity of Zn-MetAP I is increased more than 1.7-fold over Zn-MetAP I assayed in the absence of GSH. Given that the in vivo concentration of Zn(2+) is at least 1,000-fold higher than that of Co(2+), and that Co(2+) is insoluble in physiological concentrations of GSH, it is probable that yeast MetAP I is actually a Zn(2+) metalloprotease. Furthermore, unless there are extraordinary conditions that insulate or sequester them from this reducing milieu, that have yet to be identified, there are not likely to be any cytoplasmic enzymes that use free Co(2+).
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