Prolidases structure

E2. Endo, F., Tanoue, A., Nakai, H Hata, A., Indo, Y., Titani, K., and Matsuda, I., Primary structure and gene localization of human prolidase. J. Biol. Chem. 264,4476-4481 (1989). 

Next to trypsin chymotrypsin is the most preferred proteolytic enzyme in sequencing. Its specificity is less absolute than that of trypsin. Primarily the bonds that follow phenylalanine, tyrosine and tryptophan are cleaved, but measurable hydrolysis takes place next to leucine and methionine residues as well. It is advisable, therefore, to determine in preliminary experiments the conditions (enzyme-substrate ratio, time, temperature) best suited for the formation of a few and well separable fragments. Occasionally also less specific enzymes, such as pepsin, papain or thermolysin find application in structure elucidation. For the hydrolysis of specific bonds new microbial proteases can be isolated. There are known prolidases and also enzymes which hydrolyze solely the bond which follows a pyroglutamyl residue and so on. 

Most of these enz3mes contain one mole of Zn + per mole of protein, but prolidase and prolinase contain one mole of Mn +. The metal ion acts as a Lewis acid in carboxypeptidase A, establishing contact with the carbonyl group of the peptide bond which is to be cleaved. Figure 1.41 shows the arrangement of other participating residues in the active site, as revealed by X-ray structural analysis of the enzyme-substrate complex. 

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