Abstract
Vitamin B_1 is essential for growth of Euglena gracilis, a unicellular photosynthetic organism, which has both the characteristics of plant and animal. Euglena take up actively vitamin B_1 and pyrimidine moiety of thiamin, since this organism is possible to synthesize the thiazole moiety. Convertion of vitamin B_1 or the analogues to coenzyme is achieved in the participation of thiaminase II and thiamin pyrophosphokinase. In the metabolism of 2-oxo acids in E. gracilis pyruvate and 2-oxoglutarate dehydrogenase complexes are not involved, but pyruvate : NADP^+ oxidoreductase and 2-oxoglutarate decarboxylase participates in an alternative tricarboxylic acid metabolism which is composed of succinate semialdehyde dehydrogenase to catalyze further the convertion of succinate semialdehyde to succinate. Furthermore pyruvate : NADP^+ oxidoreductase is included in the wax ester fermentation which is an energy-generating system in anoxia. NAD^+ is known well to function as a cofactor in oxidation and reduction in all organisms, and further participate in metabolic regulation and signal transduction through ADP-ribosylation enzyme which catalyzes the transfer of ADP-ribose cyclase to release nicotinamide from NAD^+, according to Ca^<2+> release from intracellular Ca^<2+> stores. In Euglena a specific ADP-ribosylation to the arginine residue was shown to play an important role in S phase and G_2-M transition of cell division. Consequently polymerization of micro-tubules was completely inhibited by ADP-ribosylation in Euglena. cADP-ribose and the synthesizing enzyme, ADP-ribose cyclase, increased remarkably in the G_2 phase of cell division cycle but not inositol trisphosphate, suggesting that cADP-ribose functions as a regulator of cell division through mediating endogenious Ca^<2+> release.
