THE REDUCTION OF INORGANIC SULPHATE TO INORGANIC SULPHITE IN THE SMALL INTESTINE OF THE RAT.

1. Whole scrapings of rat intestinal mucosa were incubated with carrier-free sodium [(35)S]sulphate. Radioactivity was found in S-sulphocysteine and to a small extent in S-sulphoglutathione. 2. Whole scrapings of rat intestinal mucosa incubated with carrier-free sodium [(35)S]sulphate and oxidized glutathione formed S[(35)S]-sulphoglutathione as the main radioactive product. The amount of S[(35)S]-sulphocysteine formed was considerably lower than in a control that contained no oxidized glutathione. 3. The supernatant fraction of homogenates of rat intestinal mucosa catalyses the NADPH-dependent reduction of adenosine 3'-phosphate 5'-sulphatophosphate to inorganic sulphite. NADH or GSH fail to replace NADPH as reducing agents. 4. The formation of inorganic [(35)S]sulphite from inorganic [(35)S]-sulphate may account for the incorporation of [(35)S]sulphate into S-sulphoglutathione by the small intestine of the rat in vivo and in vitro.