Soyin, A Toxic Protein from the Soybean I. Inhibition of Rat Growth

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Abstract
The procedure for preparing purified soyin on a large scale from defatted soybean flour is described in detail. When soyin was fed to young rats at a level of 1% in a diet containing antoclaved soybean protein or casein, growth was inhibited 26% and 18%, respectively. Crude trypsin was not effective in counteracting this inhibition of growth. Equalization of food intake failed to reveal any significant differences in the growth of rats receiving diets with or without soyin. On the basis of comparable experiments with raw soybean meal in the presence and absence of crude trypsin, it is estimated that about half of the growth-inhibiting effect of raw soybean meal is due to its soyin content and the remainder to an effect which can be counteracted by crude trypsin. Growth impairment by soyin was attributed to a decrease in the quantity of food consumed.