X-Ray Interpretation of the Molecular Structure of Gelatine

Abstract

IN a recent communication¹ it was shown how X-ray studies indicate that the average dimensions associated with an amino-acid residue in an extended protein chain are of the order of 3½, 4½ and 9½ A., the first being the length in the direction of the main-chain, the second the thickness of the main-chain, and the third the lateral extension of the side-chains: it was shown also how these three quantities account for the observed average density of proteins and the weight per unit area of mono-molecular protein films. More recently² the arguments have been applied with some precision to the case of -keratin, for which the dimensions in question are found by X-rays to be 3.38, 4.65, and 9.8 A., respectively, while the density³ is 1.30 and the weighted mean residue weight about 115 (so far as can be estimated from available chemical analyses⁴). We can thus set out the following relation: which is a reasonably strict demonstration of the point we wished to make, namely, that the dimensions 3.38, 4.65, and 9.8 A. in -keratin are on the average those of one amino-acid residue.