Mechanism of phosphoacetylglucosamine mutase.

Kinetic studies of phosphoacetylglucosamine mutase (EC 2.7.5.2) for the following reactions: 1) Glc-1-P in equilibrium Glc-6-P and 2) GlcNAc-1-P in equilibrium GlcNAc-6-P have been conducted in the presence of Glc-1,6-P2 and GlcNAc-1,6-P2, respectively. In the first reaction, the initial velocity studies at various concentrations of one substrate showed a series of parallel lines in the Line-weaver-Burk plot when the concentrations of the other substrate were changed at several fixed levels. For both reactions, the initial velocity studies performed at fixed ratios of both substrates showed linear lines in the double reciprocal plot. The competitive substrate inhibition pattern was observed in the second reaction. A ping-pong mechanism is proposed for phosphoacetyl-glucosamine mutase. In addition, phosphoacetylglucosamine mutase can be phosphorylated by the addition of Glc-1-[32P]P probably via the reaction of Glc-1-[32P]P with the phosphoenzyme followed by the release of glucose-monophosphate leaving the 32P with the phosphoenzyme. The linkage between the phosphoryl residue and enzyme is stable in acid, but labile in alkali, suggesting phosphoserine (or phosphothreonine) as the phosphorylated amino acid. Biphasic heat denaturation curves suggest the existence of heat-stable and heat-labile forms of this enzyme.