Yeast sulfate-reducing system. I. Reduction of sulfate to sulfite.

X35-APS-This substrate was synthesized from S%ulfur trioxide-pyridine complex and AMP by a method similar to that of Baddiley et al. (13) except for simplifications and modifications necessary for introduction of label. An alternat,ive method has been described by Reichard and Ringertz (14). Approximately 3.7 me of S35-HzS04 was dried at 80” in a reaction tube fitted with a ball joint and side arm for gassing. Unlabeled HsS04 (3.7 mmoles, sp. gr. 1.84) was added followed by approximately 0.5 g of Pz05. Without delay, a ball joint bridge connection was made to a vented receiving flask chilled with solid COz-ethanol. Dry nitrogen gas was passed through the apparatus and the reaction tube slowly heated to 300”. The bulk of the S3503 was