HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Fee, J. A. Articles by Bull, C. Search for Related Content PubMed PubMed Citation Articles by Fee, J. A. Articles by Bull, C. Social Bookmarking                      What's this?

J. Biol. Chem., Vol. 261, Issue 28, 13000-13005, Oct, 1986

Steady-state kinetic studies of superoxide dismutases. Saturative behavior of the copper- and zinc-containing protein

JA Fee and C Bull

The mechanism of the Cu-Zn-containing superoxide dismutase (SD) was studied using a stopped-flow spectrophotometric system capable of forming aqueous solutions of O2- having initial concentrations up to approximately 5 mM. By lowering the temperature to 5.5 degrees C, we were able to observe saturation of the enzyme. At 5.5 degrees C and pH 9.3, the Michaelis-Menten parameters extracted from the kinetic traces were turnover number (TN) approximately 1 X 10(6) s-1, Km approximately 3.5 X 10(-3) M. Under our conditions, the average rate at which O-2 binds to the active site, TN/Km is 0.26 X 10(9) M-1 s-1. TN was decreased in the presence of D2O, and a solvent isotope effect of TNH/TND approximately 3.6 was measured while TN/Km was essentially unaffected by D2O. TN was increased by the presence of the general acid, ND4+. These observations, by analogy to earlier work with Fe X SD from Escherichia coli (Bull, C., and Fee, J. A. (1985) J. Am. Chem. Soc. 107, 3295-3304), suggest that H2O serves to donate the protons required to form product H2O2. Values of Km and TN for the zinc- deficient enzyme were found to be approximately a factor of 2 less than those obtained for the holoenzyme under identical experimental conditions, whereas TN/Km was largely unchanged. The imidazolate bridge is thus not essential for catalytically competent extraction of a proton from the solvent.
CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				G. Regelsberger, U. Laaha, D. Dietmann, F. Ruker, A. Canini, M. Grilli-Caiola, P. G. Furtmuller, C. Jakopitsch, G. A. Peschek, and C. Obinger The Iron Superoxide Dismutase from the Filamentous Cyanobacterium Nostoc PCC 7120: LOCALIZATION, OVEREXPRESSION, AND BIOCHEMICAL CHARACTERIZATION J. Biol. Chem., October 22, 2004; 279(43): 44384 - 44393. [Abstract] [Full Text] [PDF]

				M. K. Baum, G. Shor-Posner, and A. Campa Zinc Status in Human Immunodeficiency Virus Infection J. Nutr., May 1, 2000; 130(5): 1421S - 1423. [Abstract] [Full Text]

				J. J. Goto, E. B. Gralla, J. S. Valentine, and D. E. Cabelli Reactions of Hydrogen Peroxide with Familial Amyotrophic Lateral Sclerosis Mutant Human Copper-Zinc Superoxide Dismutases Studied by Pulse Radiolysis J. Biol. Chem., November 13, 1998; 273(46): 30104 - 30109. [Abstract] [Full Text] [PDF]

				K Sharp, R Fine, and B Honig Computer simulations of the diffusion of a substrate to an active site of an enzyme Science, June 12, 1987; 236(4807): 1460 - 1463. [Abstract] [PDF]