Amino-Acids in Staple Foods. The Role of Cystine in Proteolytic Digestion

Abstract

The author presented his views on the synthesis of amino-acids in the animal body at the Washington annual meeting of the Society of Biological Chemists in 1936 (unpublished) and concluded that cystine, contrary to the view held at that time, is a dispensable amino-acid. His working hypothesis was that sugar forming amino-acids are dispensable and non-sugar formers are indispensable, and also suggested that valine being a non-sugar former would prove to be an indispensable amino-acid. There are so many examples in the literature where the diet under investigation was supplemented with cystine which promptly converted it to a normal growth-producing one that a claim of cystine deficiency was readily granted. Johns and Finks1 fed cooked navy bean meal supplemented with cystine to rats and obtained normal growth so that they concluded that cystine deficiency was the controlling factor in the bean diet. Mitchell and Smuts'2 feeding experiments demonstrated clearly that by supplementing raw soybean meal with c...