Sulphur Metabolism of Yeast.

Two general conclusions are warranted as to the sulphur metabolism and nutrition in animals. The first is that although most of the sulphur taken into the system is in the reduced form, that is, mainly as cystine or possibly also as cysteine, nevertheless the main end product of normal sulphur metabolism is the completely oxidized sulphate form. This is well established by numerous investigations. The other important conclusion is that cystine is a very important amino acid in growth and maintenance. Recently the importance of sulphur in nutrition of plants has also been so well shown that the use of sulphates in fertilizers is emphasized. ARMSTRONG (1) also studied the effect of various sulphur compounds in the development of Aspergillus niger, Penicillium glaucurn, and Botrytis cinerea. He concluded that the best form of food sulphur is sulphate, and that even here the end product of sulphur metabolism is the sulphate form. Recent studies (7) in this laboratory indicate that cystine also may be of some importance in yeast growth and that studies on yeast, when properly controlled, may throw more light on certain phases of metabolism. The object of this investigation was to determine more definitely the forms of sulphur available for yeast growth, and to investigate further the changes cystine undergoes in yeast growth and metabolism. In all the studies here reported the concentration of the yeast growth stimulant was carefully controlled just as in the work by MILLER (5) and SWOBODA (7). In the first part of the work various forms and amounts of sulphur, as found in biological material, were added to an artificial medium containing a known, but very small amount of sulphur, and the rate of yeast growth determined by the weighing method. In the second part of the study the yeast was separated and analyzed for sulphur, and the filtrate analyzed for total sulphur and for "inorganic sulphate."