Glycyl tyrosine enzyme complex

Figure 1-6. The structure of carboxypeptidase A changes dynamically upon substrate binding. (A) Enzyme alone, (B) enzyme complex with glycyl-tyro-sine. Tyrosine 248 moves 12 A after binding of substrate. Hydrolysis results as a concerted action of Zn2+, Clu, Tyr, and Arg side chains towards the carbonyl and nitrogen group in the susceptible peptide bond (C).

Another difficulty which has faced the x-ray crystallographic approach to deciphering enzyme mechanisms is the inability to examine enzyme-substrate complexes. To circumvent this problem, complexes with inhibitors, products, or pseudosubstrates have been employed. In the case of carboxypeptidase A, mechanistic deductions have been based on results obtained using the very poor substrate glycyl-L-tyrosine (60). 

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