On the Sulphur Metabolism of Rhodotorula gracilis. I. The Importance of Sulphur and Iron for the Formation of Protein and Fat.

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Abstract
I. The fat content of the yeast Rhodotorula gracilis (I) increased from 11.8 to 36.5% while the protein content dropped from 42.5 to 13% when only the MgSO4[center dot]7H2O content of the nutrient soln. (II) was decreased from 3 to 0.03 g./l. If the FeCl3.6 H2O content of II was changed from 0.015 g./l. to 0, the fat content increased from 12.3 to 27.8% and the protein content decreased from 44.6 to 21.9%. The agreement in composition found in yeast formed with a deficiency of N, S or Fe indicates that the decisive factor in the increased fat production is the reduction in the protein content of the yeast.[long dash]II. The metabolism of the protein-poor yeast is strongly reduced compared with that of the protein-rich yeast as indicated by the reduced yield of I. Parallel with the decrease of protein content of I a decrease of the content of SH groups occurred. The ratio SH/(SH + SS) for the yeast cultivated on the substrate poor in S, determined polarographically, was I, indicating S existing only as SH.