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In vitro and in vivo regulation of assimilatory nitrite reductase from Candida utilis

Sengupta, S and Shaila, Melkote Subbarao and Rao, Gannamani Ramananda (1997) In vitro and in vivo regulation of assimilatory nitrite reductase from Candida utilis. In: Archives of Microbiology, 168 (3). pp. 215-224.

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The nitrate assimilation pathway in Candida utilis, as in other assimilatory organisms, is mediated by two enzymes: nitrate reductase and nitrite reductase. Purified nitrite reductase has been shown to be a heterodimer consisting of 58- and 66-kDa subunits. In the present study, nitrite reductase was found to be capable of utilising both NADH and NADPH as electron donors. FAD, which is an essential coenzyme, stabilised the enzyme during the purification process. The enzyme was modified by cysteine modifiers, and the inactivation could be reversed by thiol reagents. One cysteine was demonstrated to be essential for the enzymatic activity. In vitro, the enzyme was inactivated by ammonium salts, the end product of the path way, proving that the enzyme is assimilatory in function. In vivo, the enzyme was induced by nitrate and repressed by ammonium ions. During induction and repression, the levels of nitrite reductase mRNA, protein, and enzyme activity were modulated together, which indicated that the primary level of regulation of this enzyme was at the transcriptional level. When the enzyme was incubated with ammonium salts in vitro or when the enzyme was assayed in cells grown with the same salts as the source of nitrogen, the residual enzymatic activities were similar. Thus, a study of the in vitro inactivation can give a clue to understanding the mechanism of in vivo regulation of nitrite reductase in Candida utilis.

Item Type: Journal Article
Publication: Archives of Microbiology
Publisher: Springer
Additional Information: Copyright of this article belongs to Springer.
Keywords: Candida utilis;Nitrite reductase;Electron donors;Cysteine modification;Transcriptional control
Department/Centre: Division of Biological Sciences > Microbiology & Cell Biology
Date Deposited: 18 Oct 2011 04:48
Last Modified: 18 Oct 2011 04:48
URI: http://eprints.iisc.ac.in/id/eprint/38275

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