Pyrophosphate:d-Fructose 6-Phosphate 1-Phosphotransferase

Abstract

Abstract The major enzyme of Entamoeba histolytica which produces fructose 1,6-diphosphate from fructose 6-phosphate utilizes inorganic pyrophosphate as phosphate donor. In its reverse reaction the enzyme utilizes orthophosphate and fructose diphosphate to yield inorganic pyrophosphate and fructose 6-phosphate. The enzyme has been purified 100-fold from an amebal homogenate. At pH 7 with 2.5 mm MgCl the following Km values were observed: pyrophosphate, 14 µm; fructose 6-phosphate, 38 µm; fructose 1,6-diphosphate, 18 µm; and orthophosphate, 800 µm. At this pH and magnesium ion concentration the maximum velocity of the reaction was approximately the same in each direction. The average intracellular concentration of pyrophosphate in the ameba is 0.18 mm, a value 13-fold greater than the pyrophosphate Km for the new enzyme. This enzyme raises to three the number of known enzymes in the glycolytic pathway of E. histolytica which utilize or produce pyrophosphate. The trivial name proposed for the new enzyme is 6-phosphofructokinase (PPi).