Intraphagocytic beta-N-acetylglucosaminidase. Properties of the enzyme and its activity on group A streptococcal carbohydrate in comparison with a soil bacillus enzyme

Abstract

The beta-N-acetylglucosaminidases of rabbit and human polymorphonuclear leukocytes and of rabbit alveolar macrophages have been studied in comparison with the beta-N-acetylglucosaminidase derived from a soil bacillus which had previously been shown to hydrolyze the group-specific polysaccharide of Group A streptococci. The phagocytic enzymes are lysosome associated and have an acid pH optimum. In contrast, the soil bacillus enzyme is an extracellular product, has a higher pH optimum, and is probaby of smaller molecular size. When tested on p-nitrophenyl-betaN-acetylglucosaminide as substrate, the K(m) of the phagocytic enzymes is slightly higher than that of the soil bacillus. However, there were extreme differences in their effect on the Group A streptococcal polysaccharide. Thus, 5 x 10(6) units of the alveolar macrophage enzyme were required to hydrolyze the available N-acetylglucosamine of 1 mg of polysaccharide in 18 hr, while 100 units of the soil bacillus enzyme were sufficient to achieve this hydrolysis. In both cases, the serological reactivity of the polysaccharide is altered with loss of Group A specificity and acquisition of a new specificity characteristic of A-variant streptococci. Possible explanations for differences in the activity of the enzymes are considered, and the role of the phagocytic enzymes in intracellular degradation of Group A streptococci is discussed.