Four decades of studies on the isolation, characterization, properties, structure, function and possible uses of the Bowman‐Birk trypsin‐ and chymotrypsin‐inhibitor from soybeans are reviewed. Starting from Bowman's Acetone Insoluble factor, designated Ai, AA and SBTIAA, the Bowman‐Birk inhibitor (BBI) was found to be a protein molecule consisting of a chain of 71 amino acids cross linked by 7 disulfide bonds, with a tendency to self‐associate. BBI possesses two independent sites of inhibition, one at Lys 16‐Ser 17 against trypsin and the other at Leu 43‐Ser 44 against chymotrypsin. It forms a 1:1 complex with either trypsin or chymotrypsin and a ternary complex with both enzymes. Ingestion of BBI by rats, chicks or quails affects the size and protein biosynthesis of the pancreas. Establishment of the full covalent structure of BBI revealed a high homology in the sequences around the two inhibitory sites, suggesting evolutionary gene duplication from a single‐headed ancestral inhibitor. Scission of BBI by CNBr followed by pepsin results in two active fragments, one that inhibits trypsin and the other, chymotrypsin. Replacements and substitutions in the reactive sites result in changes in inhibitory activity and in specificity of inhibition. Conformation studies, labeling of BBI with a photoreactive reagent, chemical synthesis of cyclic peptides that include inhibitory sites, in vitro synthesis of BBI, and species specificity regarding the inhibited enzymes are described. The significance of BBI as a prototype of a family of inhibitors present in all legume seeds is discussed.

Two properties of soybean isoflavones were examined in in vitro systems: (1) their antioxidative potency by measuring the extent of inhibition of lipoxygenase action and (2) their antihemolytic activity by measuring their ability to prevent peroxidative hemolysis of erythrocytes. The extent of the antioxidative capacity of isoflavones is positively correlated to the number of hydroxyl groups in the isoflavone nucleus. Glycosidation of isoflavones depressed their antioxidative activity considerably. A different susceptibility of erythrocytes of sheep, rats, and rabbits to the antihemolytic activity of isoflavones was found. Very high antihemolytic activity of some isoflavones such as daidzein was exerted toward sheep erythrocytes, very little and only by genistein was exerted toward rat erythrocytes, and no antihemolytic effect was noted at all on rabbit erythrocytes. A hemolysis enhancing activity of small amounts of isoflavones on rabbit erythrocytes, but not on those of sheep and rats, has been observed. The antioxidative and antihemolytic activities of isoflavones toward sheep erythrocytes were differently affected by structural differences of isoflavones.

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