COVALENT ATTACHMENT OF AMINO-ACIDS TO CASEIN .1. CHEMICAL MODIFICATION AND RATES OF INVITRO ENZYMATIC-HYDROLYSIS OF DERIVATIVES

Active N-hydroxysuccinimide esters of various ierf-butyloxycarbonyl-L-amino acids were used to covalently attach amino acids to casein through isopeptide bonds. Tryptophan was used to determine the best conditions for the reaction; glycine, alanine, methionine, N-acetylmethionine, aspartic acid, and asparagine were also covalently linked to casein. In vitro rate studies performed with bovine a-chymotrypsin, bovine pancreatin, and rat bile pancreatic juice indicated that hydrolysis of the modified casein derivatives were lower than that of unmodified protein. The rates of decreased hydrolyses did not result from changes in solubility properties but was rather due to steric hindrance as well as conformational changes of the modified protein as shown by fluorescence and absorption spectra. The facile covalent attachment of amino acids to proteins appears to be a promising method for improving the biological value of food proteins. © 1979, American Chemical Society. All rights reserved.