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Factors Affecting Hexose Phosphorylation in Acetobacter xylinum

Department of Biological Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel

ABSTRACT

Fructose was oxidized and converted to cellulose by cells of Acetobacter xylinum grown on fructose or succinate, but not by cells grown on glucose. In resting fructose-grown cells, glucose strongly suppressed fructose utilization. Extracts obtained from fructose- or succinate-grown cells catalyzed the adenosine triphosphate (ATP)-dependent formation of the 6-phosphate esters of glucose and fructose, whereas glucose-grown cell extracts phosphorylated glucose but not fructose. Fructokinase and glucokinase activities were separated and partially purified from cells grown on glucose, fructose, or succinate. Whereas fructokinase phosphorylated fructose only, glucokinase was active towards glucose and less active towards mannose and glucosamine. The optimal pH for the fructokinase was 7.4 and for the glucokinase was 8.5. The K_m values for the fructokinase were: fructose, 6.2 mM; and ATP, 0.83 mM. The K_m values for the glucokinase were: glucose, 0.22 mM; and ATP, 4.2 mM. Fructokinase was inhibited by glucose, glucosamine, mannose, and deoxyglucose in a manner competitive with respect to fructose, with K_i values of 0.1, 0.14, 0.5, and 7.5 mM, respectively. Adenosine diphosphate (ADP) and adenosine monophosphate (AMP) inhibited both kinases noncompetitively with respect to ATP. The K_i values were: 1.8 mM (ADP) and 2.1 mM (AMP) for fructokinase, and 2.2 mM (ADP) and 9.6 mM (AMP) for glucokinase. Fructose metabolism in A. xylinum appears to be regulated by the synthesis and activity of fructokinase.