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. 1984 Dec;81(24):7767–7771. doi: 10.1073/pnas.81.24.7767

Effects of pH on the structure and function of carboxypeptidase A: crystallographic studies.

G Shoham, D C Rees, W N Lipscomb
PMCID: PMC392233  PMID: 6595659

Abstract

High-resolution crystal structures are described for carboxypeptidase A (EC 3.4.17.1) in crystals grown at pH 8.5, 9.0, and 9.5 and compared with the structure at pH 7.5. The comparison shows that in the pH range of 7.5-9.5 the enzyme structure is practically unchanged, and, most importantly, that the flexible side chain of Tyr-248 remains exclusively in the "up" position, away from the Zn atom, throughout the pH range. There is no evidence for binding of Tyr-248 to Zn at any of these pH values. We conclude that the interaction of Tyr-248 with Zn is not an essential part of the mechanism of carboxypeptidase A and that its occurrence is an artifact of chemical modification of Tyr-248. It is also suggested that Tyr-248 is not uniquely associated with the observed high pK of the enzymatic hydrolysis.

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Selected References

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