Transpeptidation transferase

Peptide bond formation occurs immediately following the dissociation of the binding factor from the ribosome. This reaction is known as transpeptidation, and the enzymatic center that catalyzes it is known as peptidyl transferase, although it promotes the conversion of an ester to a... 

The antibiotic penicillin is a transition state analog that binds very tightly to gly-copeptidyl transferase, an enzyme required by bacteria for synthesis of the cell wall (Fig. 8.18). Glycopeptidyl transferase catalyzes a partial reaction with penicillin that covalently attaches penicillin to its own active site serine. The reaction is favored by the strong resemblance between the peptide bond in the p-lactam ring of penicillin and the transition state complex of the natural transpeptidation reaction. Active site inhibitors such as penicillin that undergo partial reaction to form irreversible inhibitors in the active site are sometimes termed suicide inhibitors. ... 

Transpeptidation In transpeptidation (peptidyl transfer), the peptide bond is formed via nucleophilic displacement of the P-site tRNA of the peptidyl-tRNA by the amino group of the aa-tRNA in the A-site. The nascent polypeptide chain is thereby lengthened at its C-terminus by one residue and transferred to the A-site tRNA (Figure 13.16). The peptidyl transfer reaction is catalyzed by the peptidyl transferase ribozyme of 23S rRNA of the 50S ribosome subunit. 

Figure 6 Dependence of y-glutamyl transferase activity on IVq in an AOT-octane-water microemulsion. The figure gives activity data for three reactions catalyzed by the enzyme transpeptidation (top), autotranspeptidation (middle), and hydrolysis (bottom). Values of catalytic activity of the enzyme in aqueous solution, measured under conditions of pH optima, are shown by the dashed lines. A scale of droplet radii corresponding to the Wq scale as well as indications of the radii of the light (L) and heavy (H) subunits and of the heterodimer (L+H) are given on the upper extension line. (From Ref 39.)...

It is unclear if the transpeptidation activity represents a way for glutathione to serve as a synthetic y-glutamyl donor or is simply an insignificant transferase activity typical of many hydrolases. This enzyme probably also participates in mercapturic acid formation, and this can be viewed as a variation of the direct hydrolysis reaction in which a substituted glutathione is substrate. 

F. J. R. Hird It seems to me that one of the main functions of this 7-glutamjd transferase enzyme is that it provides employment for biochemists. Mr. P. H. Springell of Melbourne University has examined the properties of the 7-glutamyl transferase from sheep kidney in some detail. He finds that this enzyme transfers they-glutamyl group to water and to amino acids. The pH optimum for hydrolysis is about 6.0 and for transpeptidation about pH 8.5 or higher. He also finds that amino acids compete with water for the activated linkage and this competition is weaker at pH 6.0 than it is at pH 8.5. The amino acids which are the best reactors in transpeptidation are also the best competitors with water. 

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