Properties of a Mutant ofEscherichia coliwith a Temperature-sensitive Fructose-1,6-Diphosphate Aldolase

Abstract

A mutant of E. coli in which fructose-1,6-diphosphate aldolase functions at 30 C but not at 40 C was used to study the physiological effect of a specific block in the Embden-Meyerhof glycolytic pathway. Growth of the mutant at 40 C was found to be inhibited by the presence of glucose or certain related compounds in the medium. At 40 C, glucose was metabolized at 30 to 40% of the control rate and was abnormal in that glucose was converted into other six-carbon substances (probably gluconate, in large part) that were released into the culture medium. The inhibition was complete, but transient; its duration depended upon the initial amount of inhibitor added. The resumption of growth at 40 C was correlated with the further catabolism of the excreted compounds. When glycerol was used to grow the mutant at 40 C, the growth inhibition by glucose was acom-panied by cessation of glycerol metabolism. Growth on a-glycerol phosphate was not inhibited under these conditions, implicating glycerol kinase as a possible site of inhibition; no inhibition of glycerol kinase by sugar phosphates, however, could be detected in-vitro. The inhibitory effect of glucose on growth at 40 C is not caused by a deficit of intracellular adenosine triphosphate, but may be the result of ageneral-ized poisoning of many cell processes by a greatly increased intracellular concentration of fructose-l,6-diphosphate, the substrate of the damaged enzyme.