Stereochemical Studies on the Reactions Catalyzed by the PLP-Dependent Enzyme 1-Aminocyclopropane-1-carboxylate Deaminase

Abstract:

The stereochemical course of 1-aminocyclopropane-1-carboxylate deaminase which catalyzes the fragmentation of the cyclopropane substrate to α-ketobutyrate and ammonia has been unraveled with the help of substrates stereospecifically labeled with deuterium and/or tritium, and this has afforded important information about the process occurring at the active site during enzymatic conversion. These results can be summarized as follows: (1) ring cleavage is regiospecific and only occurs between the pro-S and the α-carbon of ACPC; (2) β-H abstraction is pro-R stereospecific and the reprotonation at β-C is mediated by the same enzyme base which is partially shielded and located at the si face relative to α-C; (3) preferred conformation of the β,γ-olefinic PLP-p-quinoid α-anion complex is cisoid and the geometry of the terminal double bond, if trisubstituted, favors E, while the major conformation of the nascent intermediate, aminocrotonate, is Z (defined as relative to the amino group); (4) protonation at C-4 is mediated by a different enzyme base which is not shielded and is situated at the si face with respect to α-C. © 1984, American Chemical Society. All rights reserved.

Año de publicación:

1984

Keywords:

Fuente:

scopus