The Regulation of Glycolate Metabolism in Division Synchronized Cultures of Euglena

Phosphoglycolate and phosphoglycerate phosphatases and glycolate dehydrogenase activities were determined in division synchronized Euglena gracilis strain Z cultures. Phosphoglycolate phosphatase activity remained nearly constant in the light but doubled in the dark, whereas phosphoglycerate phosphatase activity decreased by half in the light and increased 4-fold over the dark phase of the cycle. Glycolate dehydrogenase activity assayed by dye reduction increased over the light and remained constant during the dark phase, but when determined by the phenylhydrazone method, an assay dependent upon the presence of a natural hydrogen acceptor, activity decreased in the dark phase. The acceptor decayed in the dark in all cell-free extracts and 3-(3,4-dichlorophenyl)-1, 1-dimethylurea inhibited light regeneration.Enzyme activity regulated flow of carbon via the glycolate pathway; with cells at end of light phase and early dark phase, high levels of glycolate dehydrogenase activity were accompanied by an early and rapid labeling of glycerate. Degradation of early samples gave uniformly labeled glycolate and glycerate while phosphoglycerate was predominantly carboxyl labeled. At these stages in the division cycle, glycerate was formed from glycolate via the glycolate pathway, all the enzymes of the pathway being recorded in Euglena. In contrast to cells from end of dark phase and early light phase, times of maximum phosphoglycerate phosphatase activity, glycerate was predominantly carboxyl labeled as was phosphoglycerate, but glycolate was still uniformly labeled.Glycolate excretion varied over the cycle, being maximal at end of dark phase, decreasing throughout the light phase until not detectable in early dark phase. When alpha-hydroxy-2-pyridinemethanesulfonate was used as a measure of glycolate biosynthesis, sufficient glycolate dehydrogenase was present to oxidize the glycolate produced at all stages over the cycle.