Glutamate carboxylate-zinc interactions

Fig. 18. The carboxylaie-histidine-zinc triad represents indirect carboxylate-zinc interaction across bridging histidine. Both tautomers of histidine are observed, and the hydrogen bond stereochemistry with carboxylate (either aspartate or glutamate) is generally syn. Experimental results and theoretical calculations suggest that the carboxylate-histidine- zinc form may be in equilibrium with the carboxylic acid-histidinate- zinc form, as shown.

The free a-amino group of the dipeptide interacts with glutamate at position 270 the y-COOH group is involved and a water molecule is located between the amino and carboxyl groups. Interactions which directly involve the catalytic action of the enzyme are as follows (a) the carbonyl of the peptide bond ligands to a zinc atom, which itself is further bound to two histidines (positions 69,196) and a glutamate... 

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