Leucine-Isoleucine Content of Wool

Abstract

THE procedure described by Moore and Stein¹ for the chromatography of protein hydrolysates on columns of ‘Dowex 50’ permits a complete separation and estimation of leucine and isoleucine. This has not previously been possible with the methods of quantitative analysis which have been applied to wool. Martin and Synge², using a commercial merino 64's quality dry-combed top, prepared a leucine fraction from the acetylated hydrolysate by counter-current extraction. They compared the optical rotation of this fraction with the rotations calculated for pure acetyl-L-leucine and acetyl-L-isoleucine, and estimated the total amount of leucine isomers present to be 7.2 per cent (leucine nitrogen as per cent total nitrogen) and the ratio of leucine to isoleucine to be approximately 4 : 1. Graham, Waitkoff and Hier³ employed the microbiological method of Hier, Graham, Freides and Klein⁴ to analyse an unspecified grade of wool and found the leucine isomers present to account for 8.3 per cent of the total nitrogen, with a ratio of leucine to isoleucine of 1.8 : 1. The figures quoted by these workers for the fourteen amino-acids which they determined are, in general, higher than those reported elsewhere (for example, Speakman⁵).