Inhibition of the Pasteur effect in yeast by tumor extracts and differences in lability of sulfur in normal and tumor tissues.

epididymal spermatozoa. The biological activity of the extracts seemed to result, at least in part, from their ability to prevent energy utilization by uncoupling oxidative phosphorylation (8, 11). More recently, it has been possible to separate the yeast fermentation stimulating activity from that which causes uncoupling of oxidative phosphory lation in rat kidney or liver preparations. In freshly ejaculated bull semen the yeaststimulating substance appeared to be liberated slowly from the sperm cells in a more or less inac tive form (water-soluble) under the influence of certain enzyme systems present in seminal fluid; but it could readily be released in the active state from spermatozoa or whole semen by mild alka line hydrolysis and then could be extracted with nonpolar solvents. Similar yeast-active extracts were also obtained from testicular tissue. The yeast-active principle has recently been isolated in crystalline form from hog testis extract and has been identified as elemental sulfur. The sulfur pre cursor in semen, as elaborated from the sperm cells, appeared to be a nondialyzable polypeptide, other than glutathione, from which elemental sul fur might be split off by enzymes of the thionase type. These have been found present in both seminal fluid and yeast. The details of this exten sive series of investigation will be presented else where.1