Hexosamine Synthesis by Cell-free Extracts of Various Bacteria

Abstract

AN enzyme system catalysing the synthesis of glucosamine-6-phosphate from glutamine and fructose-6-phosphate or glucose-6-phosphate has been demonstrated in Neurospora crassa ^1,3, rat liver^2,3 and Escherichia coli ³. Ghosh et al. ³, who purified the enzyme from these various sources and studied its properties, have called it _L-glutamine-_D-fructose-6-phosphate transamidase. We have determined transamidase activity in fresh, cell-free extracts of Bacillus cereus, Micrococcus lysodeikticus, Aerobacter aerogenes and Escherichia coli. Results indicate that, for a given weight of cells, activity is higher in Gram-positive than in Gram-negative bacteria, and for a given organism, activity increases markedly during the lag and early exponential phases of growth, but decreases during the stationary phase. The high transamidase activity associated with dividing cells is probably related to the synthesis of cell-wall basal structure⁴, which contains amino-sugars. During these investigations, using a system with standard conditions of pH, substrate concentrations and reaction time at 37°, it was found that the amount of glucos-amine-6-phosphate synthesized rarely exceeded 25 per cent theoretical, and frequently was not proportional to enzyme concentration when different volumes of the same cell extract were tested in parallel. An attempt was made to explain these findings.