Pepsin inhibitor from roots of Anchusa strigosa.

A pepsin inhibitor of undetermined exact chemical composition was isolated from the aqueous extracts of the roots of Anchusa strigosa. The extract of 1 g dry roots inhibited 9380 +/- 390 micrograms of pepsin. The main steps of the isolation procedure consisted of extraction in boiling water, precipitation at pH 3 and washing the precipitate with ethanol, column chromatography on sephadex G-75, and finally ultrafiltration on UM10 membrane. The specific activity at the last step was 44 units ml-1 solution which measured 1.0 at 287 nm (a one unit of the inhibitor is that amount which inhibited 1 microgram of pepsin under the conditions of the assay). The overall purification was 22-fold. The inhibitor did not bind CM-cellulose, but it did bind DEAE-cellulose irreversibly. A pepsin-inhibitor complex was formed with a KI = 2 x 10(-8) M. The inhibitor inhibited peptic milk-clotting activity at pH 5.3. A solution of the inhibitor exhibited split-peak spectra with two maxima at 280 nm and 287 nm. The epsilon at 287 nm was estimated at 9.4 x 10(5) l mol-1 cm-1 based on a M(r) value which was estimated at 62,500.