Hypoxanthine-guanine phosphoribosyltransferase in human erythroid cells: Properties of the isozymes |
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Authors: | Gerald G Johnson Sharon A Nash |
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Institution: | (1) Department of Biology and Molecular Biology Institute, San Diego State University, 92182 San Diego, California;(2) Present address: Division of Research and Product Development, Upjohn Company, 49001 Kalamazoo, Michigan |
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Abstract: | We have previously given evidence that the hypoxanthine-guanine phosphoribosyltransferase (HGPRT; EC 2.4.2.8) isozymes in human erythroid cells result from posttranslational modifications of a single gene product Johnson, G. G., et al. (1982). Biochemistry 21:960]. In the present work we compare the properties of the unmodified and two major modified isozymes, which collectively account for 90% of the HGPRT enzyme activity in cell lysates. The modified isozymes differ from the parent molecule in the pH dependence of activity and in the relative utilization of the two purine base substrates, hypoxanthine and guanine. In contrast to the changes in the catalytic properties of the enzyme, the modifications have no detectable effects on the heat stability or on the equilibrium between enzyme dimers and enzyme tetramers.This work was supported by United States Public Health Service Grant 5 RO1 CA 16754-03 and by the San Diego State University Foundation. |
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Keywords: | hypoxanthine-guanine phosphoribosyltransferase (HGPRT) isozymes erythroid cells catalytic properties |
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