The Basic Amino Acids of Silk Fibroin. the Determination of the Basic Amino Acids Yielded by Proteins*

Previous investigations of the basic amino acids yielded by human hair and by wool (1, 2) showed that the keratins of these closely allied tissues yield relatively high proportions of arginine but very low proportions of hi&line; both tissues also yield high proportions of cystine. Because of this the determination of the basic amino acids presented special analytical difficulties that necessitated slight modifications in the technique employed. Available information regarding the composition of silk fibroin suggested that the unusually high proportion of monoamino acids, that results from the hydrolysis of this material, might also give rise to analytical difficulties, a study of which would be useful in the development of the methods of protein analysis. This was indeed found to be the case and the further interesting observation was made that the ratios of the yields of the three basic amino acids from silk fibroin are very closely similar to those from wool, although the total yield of bases from silk fibroin is only about onetenth of that from wool. Very little attention has been paid in the past to the basic amino acids derived from silk. Wetael, in 1899 (3), obtained a trace of histidine, and Fischer and Skita, in 1992 (4), isolated somewhat under 1 per cent of arginine. Abderhalden, in 1922 (5),