The influence of the peptide chain length on the activity of peptidyl-tRNA hydrolase from E. coli

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Abstract
The dependence of the V max and K m on the length of the peptide moiety in the peptidyl-tRNA series (Gly) n -Val-tRNA, was measured in the system peptidyl-tRNA hydrolase-peptidyl-tRNA. It was found that the K m value decreases from 7.2 × 10 −7 M for Gly-Val-tRNA to 4.6 × 10 −7 M for (Gly) 2 -Val-tRNA and to 1.7 × 10 −7 M for (Gly) 3 -Val-tRNA; further increase of the peptide chain is not followed by decrease of the K m . The V max values are 5.7 pmole/min/EU for Gly-Val-tRNA and 42 pmole/min/EU for (Gly) 3 -Val-tRNA. The enzyme activity is inhibited competitively by uncharged tRNA with a K I value of about 10 −6 M. The significance of these results described in this paper, in relation to the fact that peptides and peptide esters do not inhibit the enzyme activity, and in relation to the proposed physiological role of the enzyme, is discussed.