Extracellular alkaline proteases from alkalophilic Vibrio metschnikovii strain RH530

Alkaline proteases, named VapT and VapK, from Gram-negative alkalophilic Vibrio metschnikovii strain RH530 were purified and characterized. Both enzymes had optimum pH and temperature of 10. 5 and 60 °C, respectively. VapT and VapK retained 40 % and 80 %, respectively, of their initial activities at pH 12 after 24-h incubation at 25 °C. The half-lives of VapT and VapK were 10 min and 24 min, respectively, at pH 8 and 60 °C. Addition of Ca²⁺ extended their half-lives more than 20 fold. VapT and VapK retained over 30 % and 90 %, respectively, of their activities in the presence of 5 % SDS and 8 M urea. Analysis of amino acid composition showed that VapT contained seven cysteine residues and VapK did two. The N-terminal amino acid sequences of the proteases were determined and compared with those of Bacillus licheniformis subtilisin Carlsberg, Vibrio alginolyticus exoprotease A, and Tritirachium album proteinase K.