| Popis: |
Analogs of PPi in which the bridge oxygen is replaced by imido, methylene, or α,ω-glycol linkages are not substrates for crystalline yeast inorganic pyrophosphatase. Apparent competitive inhibition of Mg2+-activated PPi hydrolysis is observed with imidodiphosphate and with the C1 and C2 members of the α,ω-glycol diphosphate series, methanediol diphosphate and 1,2-ethanediol diphosphate. Methylene diphosphonate, two of its C-substituted derivatives, and the C3 and C4 members of the α,ω-glycol diphosphate series are not inhibitory under the conditions employed, which are near optimal for PPi hydrolysis. Specificity for inhibitors is not markedly broader than specificity for substrate, and, like substrate specificity, is maximal in the presence of Mg2+ as activating ion. No evidence could be obtained for phosphoryl transfer to any acceptor other than water. Using 32PPi in a variety of conditions, several types of assays failed to detect formation of a phosphorylated enzyme intermediate in the reaction. The results are interpreted as favoring a concerted mechanism for this enzyme. |
