Novel alkaline serine proteases from alkalophilic Bacillus spp.: purification and some properties

Abstract

Two extracellular alkaline proteases produced by an alkalophilic Bacillus isolate were purified and characterized using acetone precipitation, DEAE- and CM-Sepharose CL-6B ion exchange and Sephacryl S-200 gel filtration chromatographic techniques. Analysis of the purified proteases by SDS–PAGE revealed that both proteases, AP-1 and AP-2 were homogenous with molecular weight estimates of 28 and 29 kDa, respectively. The optimum activity of AP-1 and AP-2 were at temperatures of 50 and 55°C and pHs of 11 and 12, respectively. The enzymes were also stable in the pH range of 6.0–12.0 for a period of 4 h with and without Ca 2+ (5 mM) and temperatures of up to 50°C. The half-lives of the enzymes recorded at 50°C were 50 and 40 min for proteases AP-1 and AP-2, respectively. The inhibition profile of the enzymes by phenylmethanesulphonyl fluoride, confirmed these enzymes to be alkaline serine proteases. The purified proteases hydrolysed native protein substrates such as casein, elastin, keratin, albumin and the synthetic chromogenic peptide substrates Glu-Gly-Ala-Phe-pNA and Glu-Ala-Ala-Ala-pNA. The K m values for the purified proteases were calculated as 1.05 mM and 1.29 mM, respectively, for Glu-Gly-Ala-Phe-pNA, and 3.81 mM and 4.79 mM, respectively, for Glu-Ala-Ala-Ala-pNA as substrates. The kinetic data also indicated that small aliphatic and aromatic amino acids were the preferred residues at the P 1 position.