Inadequacy of Proteolytic Enzyme Inhibition as Explanation for Growth Depression by Lima Bean Protein Fractions

Abstract

Lima bean protein fractions that contained high in vitro trypsin-inhibiting activity and also high growth-inhibiting activity in normal diets were fed to rats on diets containing completely acid-hydrolyzed casein as the sole source of N. All diets contained 2.4% N. A modification of Kunitz'' method (1946) of isolating the globulin-trypsin inhibitor from soybeans was used to prepare a lima bean protein fraction with a high trypsin-inhibiting activity. The diets were fed to groups of albino rats for 6 days; daily records were kept of food consumption per group and wt. of the individual rats. Expts. were carried for as long as 7 wks. The lima bean fraction produced a marked depression of growth when fed at both the 1.6 and 3.2% levels. Growth rates on diets containing the inactivated, heated fractions were essentially equal to the rate on the basal diet. The growth-depressing effect of the lima bean fraction in the hydrolysate diet was equal to, or greater than, the effect in the diet containing the unhydrolyzed protein.