Zn2+ regulation of ornithine transcarbamoylase. I. Mechanism of action

Journal of Molecular Biology
S LeeL C Kuo

Abstract

Ornithine transcarbamoylase catalyzes the formation of L-citrulline from carbamoyl phosphate and L-ornithine. The anabolic enzyme from Escherichia coli is composed of three identical subunits and resembles, in both primary and quaternary structures, the catalytic unit of aspartate transcarbamoylase. However, ornithine transcarbamoylase has no regulatory subunits. Although this enzyme does not bind its substrates co-operatively, fluorescence spectroscopic experiments show that zinc adds allosterically to the free enzyme. The metal binding process is dictated by deprotonation of an enzymic group with a pKa less than 7. The saturation binding curve of the metal ion is sigmoidal and yields a Hill coefficient of 1.6 at pH 8.5 and 25 degrees C. In the absence of substrates, zinc further promotes a slow enzyme isomerization, which occurs with a first-order rate constant of 7 min-1; thus, the metal is a slow, tight-binding inhibitor. The isomerized enzyme is inactive and contains three zinc ions. When the enzyme is first bound with carbamoyl phosphate, steady-state kinetic assays reveal that zinc again binds co-operatively to the binary enzyme complex, with a Hill coefficient of 1.5, but the metal ion now behaves simply as a classical,...Continue Reading

References

Jun 1, 1979·Archives of Biochemistry and Biophysics·R H Marks, R D Miller
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Citations

Apr 16, 1998·Biochimica Et Biophysica Acta·L E Parmentier, J S Kristensen
Sep 2, 1997·Proceedings of the National Academy of Sciences of the United States of America·Y HaN M Allewell
Dec 29, 2009·Cardiovascular Psychiatry and Neurology·Yogesh Dwivedi, Ghanshyam N Pandey
Jun 28, 2014·Biomolecules·Nicholas J Pace, Eranthie Weerapana
Jan 7, 2017·International Journal of Biological Macromolecules·Camila Pereira BragaPedro de Magalhaes Padilha
Jul 29, 2003·The Journal of Biological Chemistry·Zoran Minic, Guy Herve
Jan 5, 1990·Journal of Molecular Biology·L C KuoW Herzberg

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