Creatinase or creatine amidinohydrolase (3.5.3.3) catalyses the conversion of creatine and water to sarcosine and urea. The enzyme works as a homodimer, and is induced by choline chloride. Each monomer of creatinase has two clearly defined domains, a small N-terminal domain, and a large C-terminal domain.

The structure of the C-terminal region represents the "pita-bread" fold. The fold contains both alpha helices and an anti-parallel beta sheet within two structurally similar domains that are thought to be derived from an ancient gene duplication. The active site, where conserved, is located between the two domains. The fold is common to methionine aminopeptidase (3.4.11.18), aminopeptidase P (3.4.11.9), prolidase (3.4.13.9), agropine synthase and creatinase (3.5.3.3). Though many of these peptidases require a divalent cation, creatinase is not a metal-dependent enzyme [1, 2, 3].

1. Sequence and structure comparison suggest that methionine aminopeptidase, prolidase, aminopeptidase P, and creatinase share a common fold. Proc. Natl. Acad. Sci. U.S.A. 91, 2473-7
2. Structure of creatine amidinohydrolase from Actinobacillus. Acta Crystallogr. D Biol. Crystallogr. 58, 1322-8
3. Structure of the cobalt-dependent methionine aminopeptidase from Escherichia coli: a new type of proteolytic enzyme. Biochemistry 32, 3907-12

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