[Thiol-dependent serine proteinase from Streptomyces thermovulgaris]

The cultural filtrates of S. thermovulgaris contain a proteinase which is active towards the chromogenic subtilisin substrate, Z-Ala-Ala-Leu-pNa, and azocasein. Pure enzyme preparations were obtained by affinity chromatography on bacitracin-Sepharose with subsequent rechromatography on the same adsorbent. The proteinase was completely inactivated by PMSF and DFP, the specific inhibitors for serine proteinase, by thiol reagents (HgCl2, PCMB) and by the protein inhibitor from S. jantinus. The pH activity optimum for the enzyme is 7.8-8.2, temperature optimum is 55 degrees C. The enzyme is stable at pH 6-9, has a pI of 5.0 and a molecular mass of 32 kDa. When tested against the peptide substrate, the enzyme shows a specificity characteristic for subtilisins. The N-terminal sequence of the enzyme, Tyr-Thr-Pro-Asn-Asp-Pro-Tyr-Phe-Ser-Ser-Arg-Gln-Tyr-Gly, shows a 100% homology with that of terminase, a thiol-dependent serine proteinase. On the basis of the above considerations the enzyme may be related to the subfamily of thiol-dependent serine proteinases.