AN EXPERIMENTAL-STUDY ON CARBON FLOW IN ESCHERICHIA-COLI AS A FUNCTION OF KINETIC-PROPERTIES AND EXPRESSION LEVELS OF THE ENZYME PHOSPHOGLUCOMUTASE

Mutants of Escherichia coli deficient in phosphoglucomutase accumulate amylose when the cells are grown on maltose or galactose as carbon so urce. In the presence of physiological levels of phosphoglucomutase, m ost of the sugar is catabolized, leading to strongly reduced levels of amylose accumulation. By varying the expression level of heterologous phosphoglucomutase, we show that the minimum level needed to block am ylose accumulation corresponds to a phosphoglucomutase activity of 150 -600 nmole substrate transformed per min per mg of total soluble prote in. Mutant phosphoglucomutases with strongly reduced V-max values and increased Km values for the substrate glucose-1-phosphate or the co-su bstrate glucose-1,6-diphosphate, could also reduce amylose accumulatio n, but much higher enzyme expression levels were required. (C) 1998 Jo hn Wiley & Sons, Inc.