The Amino Acids of Alfalfa as Revealed by Paper Chromatography with Special Reference to Compounds Labelled with S.

This investigation is essentially a collaboration between two laboratories bringing together problems in which each is interested. The Department of Agricultural Research of the American Smelting and Refining Company has long been interested in the problems of sulphur toxicity and sulphur metabolism in plants which are economically important. In the course of this work investigations have been made by the use of S35. These have shown the general distribution of the isotope in the plant body. To some extent chemical procedures have been employed to identify in the protein hydrolysate specific sulphur-containing compounds, notably cystine and probably methionine (8, 9, and 10). It remained, however, necessary to obtain unequivocable evidence on the sulphur compounds into which the isotope had entered. In the Department of Botany at Rochester, investigations have been in progress since 1946 utilizing the techniques of paper chromatography to identify the free and combined amino acids in plants (2, 6, and 7). The sulphur-containing amino acids present rather special problems. Due to the small quantities commonly present and the poor reactivity of these substances with ninhydrin, they tend to be less easily detectable by the methods of paper chromatography than many of the other amino acids (1). Furthermore, as two-directional paper chromatograms are commonly carried out (i.e., using phenol: collidine-lutidine), the sulphur-containing amino acids tend to be obscured by others which are commonly present. Methionine sulphoxide occupies the same area as y-amino butyric acid, a newly discovered free amino acid which is widely distributed (4, 6, and 7). Methionine itself is close to the leucines, and cystine can best be recognized if it is first converted to cysteic acid which occupies a posit-ion on the chromatograms well apart from other amino acids (1). In these circumstances the use of S35 combined with autoradiographs of paper chromatograms is an obvious device to aid in the identification of the sulphur-containing amino acids. In the laboratories of the American Smelting and Refining Company alfalfa plants were treated with S35 in the form of sulphate. The alfalfa