Biomphalaria glabrata: Lysozyme activities in the hemolymph, digestive gland, and headfoot of the intermediate host of Schistosoma mansoni

Abstract

Lysozyme (mucopeptide N-acetylmuramylhydrolase EC 3.2.1.17) activity has been found in the hemolymph, digestive gland, and headfoot extracts of Biomphalaria glabrata, the intermediate host of Schistosoma mansoni. Partial purification of the bacteriolytic enzyme was attained by gel chromatography on Sephacryl S-200 and active lytic fractions were concentrated by Amicon filtration. The properties of the lytic enzymes from the three tissue extracts were identical. Enzyme activity was determined by the rate of lysis of cell wall suspension of Micrococcus lysodeikticus. Lysis of the cell walls was accompanied by a release of reducing sugar groups and N-acetylhexosamines. The enzyme was stable to heating at 100 C for 2 min and had an optimum activity at pH 4.5 to 5.0 in 0.066 M glycylglycine buffer. Low concentrations (5 m M) of NaCl, KCl, and LiCl increased the activity of the enzyme, whereas high concentrations (25 m M) of the same ions caused about 50% inhibition of the enzyme activity. MgCl 2 and CaCl 2 also inhibited the enzyme activity. Addition of 1 m M EDTA or EGTA resulted in about a twofold increase in enzyme activity. Double reciprocal plots of enzyme velocities and substrate concentrations yielded an apparent Michaelis-Menten constant ( K m ) of 0.05 ± 0.01 mg/ml of M. lysodeikticus.