During the next year the following work objectives will be undertaken. Conversion of 5-thio-D-fructofuranose to its 6-phosphate by yeast hexokinase will be examined. 5-Thio-D-glucose is not a substrate for commercial glycoisomerase (xyloisomerase); so the preparation of additional amounts of 5-thio-D-fructofuranose will be attempted by alkaline isomerization of 5-thio-D-glucose rather than employ the long but direct chemical synthesis formerly used. The inhibitory mechanism by which 5-thio-D-glucose affects spermatogenesis in mice and rats will be examined with attention devoted to the key glycolytic enzymes in germ cells. 5-Thio-D-glucose 1-phosphate will be examined as a substrate and possible inhibitor to glycogen phosphorylase a and b. The interaction of uridine diphosphate 5-thio-D-glucose with glycogen synthetase will be further examined. BIBLIOGRAPHIC REFERENCES: Use of a Structural Analog in the Study of Potato Phosphorylase. Minshen Chen and Roy L. Whistler, Int. J. Biochem., 7, 433-437 (1976). Biochemistry of 5-Thio-D-glucose. Minshen Chen and Roy L. Whistler, Misc. Papers, Landbouwhogeschool Wageningen, The Netherlands, H. Veenman and Zonen, B.Y., 13, 17-28 (1976).