X-Ray Studies of Protein Structure

Abstract

ACCORDING to the classical researches of Fischer and others, proteins would appear to be essentially polypeptides, giant molecules formed by the repeated condensation of a-amino-acids. This concept leads naturally to the idea of long chain-molecules like that of cellulose, the structure of which was worked out some years ago by a particularly happy combination of chemical and X-ray methods1. Similar methods applied to one of the simplest proteins, fibroin, the fibre substance of natural silk, show that, for silk at least, the hypothesis is substantially correct1; that, in fact, this fibre is a kind of molecular yarn or sliver built up by chain-like molecules, fully-extended polypeptides, lying roughly parallel to the fibre axis. The approximate dimensions of these chain-molecules may be predicted from atomic data already available, and they are found to fit in well with the results of X-ray analysis.