Characterization of Ca-activated cell-bound proteinase from Virgibacillus sp. SK37 isolated from fish sauce fermentation

Cell-bound proteinase from Virgibacillus sp. SK37 isolated from the first month of fish sauce fermentation was characterized. The enzyme showed the maximum activity at 65 °C, pH 7.0 and 9.5, using azocasein as a substrate. The enzyme required at least 10 mmol/l Ca²⁺ to effectively hydrolyze casein and the extent of casein degradation increased with Ca²⁺ concentration. Ethylenediaminetetraacetic acid (EDTA) and phenylmethanesulfonyl fluoride (PMSF) largely inhibited the activity, indicating a characteristic of Ca²⁺-activated serine proteinase. Among six synthetic substrates tested, the enzyme preferably hydrolyzed Suc-Ala-Ala-Pro-Phe-AMC, indicating a subtilisin-like proteinase. Although activity towards actomyosin at 20 g/100 ml NaCl decreased to 63% compared to at 5 g/100 ml, the enzyme showed high stability at 25 g/100 ml NaCl, 30 °C. This was the first study to report biochemical characteristics of cell-bound proteinase from a moderately halophilic bacterium isolated from fish sauce.