Intracellular serine protease from Bacillus subtilis. Structural comparison with extracellular serine proteases-subtilisins

Summary Intracellular serine protease was isolated in a pure state from sporulating Bacillus subtilis A-50. The enzyme has the molecular weight about 30.000 daltons and pI 4.3, is completely inhibited with phenylmethylsulfonyl fluoride and EDTA, and possesses a rather low activity against protein substrates, but high specific activity with subtilisin chromogenic substrates. Amino acid composition shows higher level of Glx, Lys and Phe residues and lower content of Val residues in comparison with known subtilisins. N-terminal sequence of the enzyme, being two residues shorter from N-terminus than subtilisin BPN', is NH 2 - Ser -Leu- Pro -Glu- Gly -Ile-X-Val- Ile-Lys-Ala-Pro -Glu- Leu -Gln-Ala- Gln-Gly -Phe-Lys-(residues identical with BPN' are underlined). This clearly indicates the presence of two homologous structural genes, for intra- and extracellular serine proteases, in B.subtilis genome.