Vegetative Isozyme of N-Acetylglucosaminidase in Dictyostelium discoideum

A minor isozyme of N -acetylglucosaminidase was isolated from growing cells of Dictyostelium discoideum and purified more than 1000-fold. The minor isozyme could be distinguished from the major, stage-specific isozyme which accumulates shortly after the initiation of development by its thermostability, sensitivity to heavy metals, and pH optimum. The specific activity of the minor isozyme on p -nitrophenyl-β- d - N -acetylglucosaminide is approximately one-tenth that of the stage-specific enzyme in bacterial grown cells and remains constant throughout development. However, the minor isozyme is considerably more active than the major isozyme when either bacterial murein or polymeric N -acetylglucosamine is used as the substrate. The minor isozyme is unaffected by mutations which inactivate or render thermolabile the major isozyme. Because these mutant strains grow well with bacteria as the food source, it appears that vegetative functions are carried out by the minor isozyme rather than by the major isozyme.