Insights into acylphosphatase structure and catalytic mechanism
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Acylphosphatase is one of the smallest enzymes known (about 98 amino acid residues). It is present in organs and tissues of vertebrate species as two isoenzymes sharing over 55% of sequence homology; these appear highly conserved in differing species. The two isoenzymes can be involved in a number of physiological processes, though their effective biological function is not still certain. The solution and crystal structures of different isoenzymes are known, revealing a close packed protein with a fold similar to that shown by other phosphate-bind ing proteins. The structural data, together with an extended site-directed mutagenesis investigation, led to the identification of the residues involved in enzyme catalysis. However, it appears unlikely that these residues are able to perform the full catalytic cycle: a substrate-assisted catalytic mechanism has therefore been proposed, in which the phosphate moiety of the substrate could act as a nucleophile activating the catalytic water molecule.
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