Comparison of spectral and structural properties of three homologous dimeric proteins.

Spectroscopic and structural properties of three homologous dimeric inhibitors of microbial origin, Streptomyces subtilisin inhibitor, alkaline proteinase inhibitor and plasminostreptin, were discussed by comparing the hydropathy maps, the secondary structure contents obtained from the CD analysis, and the Chou and Fasman prediction. The major process of thermal denaturation of these proteins was the two-step transition. The denaturation temperature dropped in the order Streptomyces subtilisin inhibitor greater than alkaline proteinase inhibitor greater than plasminostreptin. Differences in the denaturation temperature were interpreted in terms of differences in the hydropathy scale of side-chains of the alpha 1-helix of these proteins. The lower CD change upon the complex formation of plasminostreptin with subtilisin BPN' than those with of Streptomyces subtilisin inhibitor and alkaline proteinase inhibitor was explained in terms of the large increase in hydrophilicity of the contact region of plasminostreptin with the enzyme.