PMID: 6109547Dec 9, 1980Paper

Substrate-mediated inactivation of urocanase from Pseudomonas putida. Evidence for an essential sulfhydryl group

Biochemistry
L H Matherly, A T Phillips

Abstract

Incubation of urocanase from Pseudomonas putida with either its substrate, urocanic acid, or product, 4'(5')-imidazolone-5'(4')-propionic acid, resulted in an oxygen-dependent inhibition of enzyme activity. Coincident with the inactivation was the stoichiometric incorporation of radioactivity from [14C]urocanate into the protein. NAD+ which is required for activity or urocanase was not directly involved in the inactivation process. The inactivation of urocanase was irreversible, could be partially blocked by the competitive inhibitor imidazolepropionate, and involved the modification of a single active-site thiol. The inhibition resulted from oxidative decomposition of 4'(5')-imidazolone-5'(4')-propionate but was not due to the formation of the major degradative product, 4-ketoglutaramate, since this compound was not an irreversible inactivator of urocanase although it did produce some inhibition at high concentrations. A mechanism is presented in which a reactive imine intermediate in the decomposition scheme is subject to nucleophilic attack by an active-site thiol, thereby generating a covalent enzyme--thioaminal adduct. These results emphasize the importance of a catalytic center sulfhydryl group for urocanase activity.

Citations

Jun 1, 1989·Journal of Photochemistry and Photobiology. B, Biology·P S O'Donnell, D H Hug
Apr 15, 1989·European Journal of Biochemistry·M A SchwallerG Dodin
Aug 31, 2012·Microbiology and Molecular Biology Reviews : MMBR·Robert A Bender
Jul 29, 1991·FEBS Letters·M FessenmaierC Schubert
Jan 1, 1983·Archives of Biochemistry and Biophysics·L H Matherly, A T Phillips
Aug 18, 2004·Journal of Molecular Biology·Dirk KesslerGeorg E Schulz
Jan 26, 2021·Journal of Bioscience and Bioengineering·Daisuke MatsuiYasuhisa Asano

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