The Effect of Supplemental Methionine on the Nutritive Value of Diets Containing Concentrates of the Soybean Trypsin Inhibitor

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Abstract
Animal experiments involving measurement of the growth performance of rats were conducted to determine the effect of supplemental methionine on diets containing a soybean trypsin inhibitor concentrate and in which the sources of nitrogen were raw or autoclaved soybean protein, soybean protein hydrolysate, or casein. When the soybean hydrolysate or casein was furnished in the diet, the depression in growth exerted by the trypsin inhibitor preparation was not related to interference with the availability of methionine for growth. The beneficial effect of methionine in this instance could be wholly accounted for by the fact that the hydrolysate and casein were deficient to some extent in this amino acid. With diets containing autoclaved soybean meal, the growth-retarding action of the inhibitor was referable to interference with the availability of methionine for growth, as well as to the deficiency observed in the case of the hydrolysate and casein. These results may be explained by postulating a two-fold mode of action by active trypsin inhibitor preparations, one which results in an impairment of the availability of methionine for growth as a consequence of its antiproteolytic activity, and the other having an effect unrelated to the inhibition of proteolysis. The former can be demonstrated if the source of ingested N is an intact protein critically deficient in methionine. The latter effect is independent of the nature and quality of ingested N.