Activation of amino-acids in relation to the synthesis of silk proteins.

Abstract

THE ‘activation’ of the carboxyl groups in amino-acids is often assumed to be an indispensable preliminary stage in the biosynthesis of protein. The rate of the activation is known to vary with various amino-acids. The question arises whether there is any relation between the rate of activation of an amino-acid and its content in the protein. The silk-glands of the silkworm lend themselves particularly well to the study of such a problem since they produce two well-defined proteins, the amino-acid composition of which is known. While the posterior silk-gland produces ‘fibroin’, which contains 42 per cent of glycine and 28 per cent of alanine, the middle silk-gland produces ‘sericin’ containing 30 per cent of serine1. We have studied the activation of a number of amino-acids present in these two proteins of the silkworm caterpillars (Bombyx mori L.). The ‘pH 5 enzymes’ were obtained from the posterior and middle silk-glands as well as from the haemolymph. The hydroxamic method was used to determine the rate of the activation of the carboxyl groups in the amino-acids. The composition of the enzymatic mixture was approximately the same as that referred to by Davie, Koningsberger and Lipmann2. The results which we obtained are given in Table 1.