The Biological Activity of α-1-Antichymotrypsin: The Change of Chymotrypsin-Inhibitory and Immunoenhancing Activities by Heat Treatment1

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Abstract
The relationship between chymotrypsin-inhibitory and immunoenhancing activity of α-I-antichymotrypsin was studied. α-1-Antichymotrypsin was treated at 50°C, 55°C or 60°C for 15 min. It was found that antichymotryptic activity was reduced by half when α-1-antichymotrypsin was heated at 55°C and was not detected at all when heating was carried out at 60°C. α-1-Antichymotrypsin which was heated at 60°C did not form a complex with chymotrypsin, but became a substrate for chymotrypsin. The effect of native and heated α-1-antichymotrypsin on antibody response was studied in mice. α-1-Antichymotrypsin increased the number of anti-sheep erythrocytes antibody producing cells even when it was heated at 60°C. Circular dichroism and single radial immunodiffusion were used to detect conformational changes. Circular dichroism in the region of side chain absorption showed that the intensities of the spectra at 296, 284, and 265 nm decreased with a rise in temperature from 50 to 60°C. In single radial immunodiffusion analysis, α-1-anti-chymotrypsin did not form a halo after being heated at 60°C. In conclusion, when α-1-antichymotrypsin was heated at 60°C, the immunoenhancing activity remained intact while the antichymotryptic activity was lost with the conformational change.