CONVERSION OF ASPARTIC ACID TO GLUCOSE DURING CULMINATION IN DICTYOSTELIUM-DISCOIDEUM

Incorporation of [4C]aspartate into alkali-insoluble carbohydrtae of the cellular slime mold Dictyostelium discoideum during culmination was used to evaluated the contribution of gluconeogenesis to polysaccharide synthesis. Bacterial and chemical degradation of glucose released by cellulase digestion of the alkali-insoluble carbohydrate indicated that 84% of the 14C incorporated from [I-14C] aspartate was localized in the C-3 and C-4 positions of glucose and implicated glycolysis as the major pathway in gluconeogenesis. Greater randomization of label from [I-14C]aspartate was evident in glucose from trehalose, 73% being in the C-3 and C-4 positions of glucose. Slime mold undergoing culmination in the presence of a concentration of iodoacetate sufficient to decrease incorporation of [14C]aspartate into polyasccharide by 50% exhibited no inteference with morphogenesis and only a slight delay in the rate of development. Approximations of teh rate of incorporation of intracellular [14C]aspartate into alkali-insoluble carbohydrate gave values of 3 nmoles/min per ml cells or less, equivalent to less than 5% of the total rate of glucose conversion to polysaccharide during culmination. An indirect calculation of the minimal specific activity of the intracellular asparate pool from the specific activities of protein and nucleic acid indicated that less than 2% of the alkali-insoluble carbohydrate in the sorocarp was derived from aspartate. It is concluded that some gluconeogenesis from aspartate does occur but that it is not an essential source of the glucose utilized for stalk-building. © 1969.