CONTROL OF PEPTIDE DEFORMYLASE ACTIVITY BY METAL-CATIONS

Previous work indicated that peptide deformylase behaves as a metalloe nzyme since the Escherichia coli enzyme was shown to copurify with a z inc ion. The present study establishes that nickel:enzyme complexes ca n also be isolated provided that nickel salts were added in the buffer s throughout the purification. Similar results were obtained with the deformylases from Thermus thermophilus and Bacillus stearothermophilus . As a result of nickel binding, the catalytic efficiencies of peptide deformylases increased by two to three orders of magnitude with respe ct to those of the forms previously characterized. Using the model sub strate N-formyl-Met-Ala-Ser, k(cat)/K-m values of 5.4, 1.2 and 25 10(4 ) M-1 s(-1) could be obtained for the E. coli, T, thermophilus and B, stenrothermophilus enzymes, respectively. This value satisfyingly acco unts for the deformylation turn-over required in the cell. In vitro ch aracterization of the E. coli enzyme shows that zinc can readily subst itute for the bound nickel with the catalytic efficiency decreasing to 80 M-1 s(-1) in turn. Conversely, the activity of the zinc-containing protein can be significantly improved by addition of nickel to the en zymatic assay. (C) 1998 Academic Press.