Endoenzyme

Abstract: Enzymes dissociated from corn (hybrid B73 × Mo17) seedling cell walls by solutions of high ionic strength possess the capacity to degrade Avena caryopsis glucan. Inhibitor studies disclosed that both endo- and exoenzyme activities were involved and that the reaction sequence paralleled the autolytic solubilization of β-d-glucan in isolated cell walls. The salt-dissociated exoenzyme activity was strongly inhibited by HgCl 2 and to a lesser extent by parachloromercuribenzoate at a concentration of 100 micromolar. In the absence of these inhibitors, Avena caryopsis glucan was converted to monosaccharide, whereas in the presence of the mercurials, only endoenzyme activity was apparent and the glucan substrate was hydrolyzed yielding products with an average molecular size of 1.5 to 3.0 × 10 4 daltons. Endoenzyme hydrolysis of the caryopsis glucan could not be attributed to the participation of an enzyme specific for mixed-linkage substrates. The autolytic capacity of isolated cell walls was similarly affected by inhibitors. In the presence of 100 micromolar HgCl 2 , cell walls released from 60 to 80 micrograms per milligram dry weight as polymeric glucan during a 24-hour period. Monosaccharide accounted for less than 2% of the autolytically solubilized products. Analysis of the polymeric glucan product revealed a similarity in molecular size to the products obtained following treatment of Avena caryopsis glucan with salt-dissociated wall protein. The results suggest that among the salt-dissociated proteins are those responsible for the autolytic capacity of isolated cell walls.

Abstract: β-N-Acetylglucosaminidase has been purified from the walls of Bacillus subtilis 168 and compared with the other known autolysin, N-acetylmuramyl-L-alanine amidase (amidase). The β-N-acetylglucosaminidase was a dimer in LiCl buffers with a sub-unit molecular weight of 90000 and a pH optimum of about 5.0. It was very sensitive to proteolytic enzymes and was critically activated by 0.1 to 0.2 M-LiCl. It was insoluble in concentrations of LiCl lower than 0.05 to 0.1 M. It was less strongly bound to walls than was the amidase, which was a monomer of molecular weight 30000 to 40000 in LiCl buffers. The β-N-acetylglucosaminidase is an endoenzyme and showed no exo-activity. Lysozyme-like enzyme (muramidase) activity was undetectable in the wall extracts examined.

Abstract: Seventeen strains of lactic acid bacteria were assayed for their glycerol ester hydrolase activity by using an improved agar-well technique, and eight strains by determining the activity in cell-free extracts using a pH-stat procedure. All cultures tested showed activity and hydrolyzed tributyrin more actively than they did tricaproin. The cell extract studies demonstrated that the cells contained intracellular esterases and lipases. The culture supernatant fluid was without activity. The lipase and the esterase differed in their relative activity to each other in the different extracts and in the ease by which they could be freed from the cellular debris. It is suggested that the lipase of these organisms is an endoenzyme and the esterase an ectoenzyme.