Kinetic and molecular properties of Bacillus subtilis IBTC-3 subtilisin

Abstract

Bacillus subtilis IBTC-3 subtilisin was purified by gel filtration on Sephadex G 75 and affinity chromatography on bacitracin–CNBr-Sepharose 4B and characterized. Its molecular mass of 27 kDa was determined by SDS–PAGE, and isoelectric pH of 8.4 by chromatofocusing. FT-Raman and FT-IR spectroscopy studies revealed fragments with α-helix and irregular secondary structures within the polypeptide chain. The β-sheet conformation was observed only in second-derivatives of FT-RS and FT-IR spectra, in the range of the amide II, III, and I bands. Tyr residues were shown to be hydrogen bonded and C S CH 3 groups adopted two conformations (P H-T and P C-G conformers). Kinetic properties of B. subtilis IBTC-3 subtilisin in hydrolysis of ethyl esters of amino acid derivatives were compared with that of alkaline peptidase from Bacillus alcalophilus PB92. The first enzyme displayed the highest affinity for NAc-Phe-OEt, both in hydrolysis ( K m of 0.22 mM) and in synthesis ( K m of 0.85 mM), whereas PB92 peptidase preferred Tyr derivatives (NAc-Tyr-OEt, K m of 0.043 and 0.75 mM, respectively). In contrast to the latter enzyme, B. subtilis IBTC-3 subtilisin catalyzed hydrolysis and synthesis of Bz-Arg-OEt.