A new sulphur-containing amino acid isolated from casein

Abstract

In a report on a study of the cultural requirements of streptococci made last year before this society, the writer stated that a compound containing sulphur had been isolated from casein, which was apparently not related to cystine, and which seemed to be required for the growth of the test organisms. Although subsequent work has shown that this sulphur compound, when pure, is apparently not concerned in the growth of streptococci, it seemed desirable to make a study of the substance, both because of the uncertainty of the nature of non-cystine protein sulphur, and also in order to be able to effect a separation of this compound from the bacterial growth inducing factor in the amino acid fraction under investigation. While there are still many points to be cleared up in connection with the substance, perhaps enough information has been obtained to warrant a preliminary report.

There have been a number of difficulties met with in the work. The yield is very small, and probably not by any means quantitative, and further, no insoluble compounds suitable for separation have so far been found, so that purification has consisted largely in methods for the removal of impurities.

In order to obtain sufficient material for analyses, thirty pounc-ls of cormnercial Argentine casein were used. Briefly, the method consists in hydrolysis with sulphuric acid, neutralization with sodium carbonate, and piecipitation with mercuric sulphate solution. From the washed precipitate, freed from electrolytes, a considerable quantity of other material is removed by a second precipitation with nlercuric sulphate, the sulphur compound this time remaining in the filtrate. Further purification is effected by precipitation of the filtrate, after removing electrolytes, by silver sulphate and barium hydroxide, and the compound itself is obtained from the silver filtrate, freed, of course, from Ag and Ba, by fractional crystallization, finally from dilute acetone.