Variation of enzyme activities at a branched pathway involved in the utilization of gluconate in escherichia coli

Twenty-four strains of Escherichia coli from the ECOR collection were characterized for growth rate in gluconate minimal salts medium and for V_max and K_m of the three enzymes (gluconokinase, 6-phosphogluconate dehydrogenase, and 6-phosphogluconate dehydratase) that form a branch point for the utilization of gluconate. A total of 11 characters - growth rate, three V_max values, four K_m values, and three V_max/K_m values - were determined for these 24 ECOR strains. Most of the characters were normally distributed. Statistical tests showed that growth rate is significantly less variable than enzyme activities. Also, analyses of variance showed significant differences among strains and among the extant five genetic groups of E. coli for the characters measured. A Mantel test showed that, for some characters, closely related strains shared similar character values. Two hypotheses regarding the relationships between growth rate and enzyme activity and between various enzyme activities were tested. None of the expected correlations between growth rate and enzyme activity or between enzyme activities was detected. The results were discussed in terms of metabolic control analysis and neutral theory.