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Esterases of Micrococcus Species: Identification and Partial Characterization

Dapartment of Food Science and The Food Research Institute, University of Wisconsin-Madison, Madison 53706

Five different strains or species of micrococci were examined for intracellular esterase activity using various chromogenic ortho (o)- and para (p)-nitrophenyl derivatives of fatty acids as substrates. All strains possessed esterase activity, and p-nitrophenyl derivatives of fatty acids were hydrolyzed faster than o-nitrophenyl derivatives by all strains except Micrococcus caseolyticus ATCC 13548, which hydrolyzed o-nitrophenyl propionate faster than p-nitrophenyl propionate and both o- and p-nitrophenyl caprate at an equal rate. Active esterases in cell-free extracts were separated, identified, and their specificity toward various - and -naphthyl esters of acetic, propionic, and butyric acids were determined by histochemical staining followed by PAGE. Preparations from all strains exhibited several active bands of esterases on gels, but there was no similarity in relative mobility values of esterases among the strains. The esterase in a crude cell-free extract of Micrococcus species ATCC 8459 was partially characterized using p-nitrophenyl acetate and butyrate as substrates. The esterase had optima at pH 8.0 and 40°C. Esterase activity was inhibited by several divalent metal ions; was strongly inhibited by eserine, diisopropyl fluorophosphate (DFP), and sodium fluoride; and was slightly inhibited by 1,10-phenanthroline and sodium taurocholate. Enzyme activity was markedly inhibited by sodium chloride at pH 7.0 and was completely inhibited at pH 5.0. The activity also was strongly inhibited by reducing and oxidizing agents.