The role of Mg ions in the hypoxanthine guanine phosphoribosyltransferase-catalyzed reaction have been studied using accurate values of proton and Mg stability constants of phosphoribosylpyrophosphate (P-Rib-PP) determined from pH titration data. The results obtained favor the conclusion that the dimagnesium salt of P-Rib-PP is the true substrate of the enzyme. The other specoiefs P -Rib-PP do not appreciably affect the initial reaction rate. The inhibition of the hypoxanthine guanine phosphoribosyltransferase-catalyzed reaction observed at highM gClz concentration can be attributed to a competitive inhibition of M&' with respect to the dimagnesium salt of P-Rib-PP, suggesting that these ionic specbiiensd to the same enzyme form. At a fixed [P-Rib-PP,,,], the concentration of its dimagnesium complex is a sigmoidal function of M&Iz concentration, suggesting that caution must be employed in the interpretation of sigmoidal saturation curves for P-Rib-PP-utilizing enzymes when low and not constant concentrations of the divalent cation are used
Human hypoxanthine guanine phosphoribosyltransferase. The role of magnesium ion in a phosphoribosylpyrophosphate-utilizing enzyme / Salerno, Costantino; Giacomello, Alessandro. - In: THE JOURNAL OF BIOLOGICAL CHEMISTRY. - ISSN 0021-9258. - STAMPA. - 256:8(1981), pp. 3671-3673.
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Titolo: | Human hypoxanthine guanine phosphoribosyltransferase. The role of magnesium ion in a phosphoribosylpyrophosphate-utilizing enzyme. | |
Autori: | ||
Data di pubblicazione: | 1981 | |
Rivista: | ||
Citazione: | Human hypoxanthine guanine phosphoribosyltransferase. The role of magnesium ion in a phosphoribosylpyrophosphate-utilizing enzyme / Salerno, Costantino; Giacomello, Alessandro. - In: THE JOURNAL OF BIOLOGICAL CHEMISTRY. - ISSN 0021-9258. - STAMPA. - 256:8(1981), pp. 3671-3673. | |
Handle: | http://hdl.handle.net/11573/24984 | |
Appartiene alla tipologia: | 01a Articolo in rivista |