Glycolate Pathway in Algae

Abstract

No glycolate oxidase activity could be detected by manometric, isotopic, or spectrophoto-metric techniques in cell extracts from 5 strains of algae grown in the light with CO2. However, NADHglyoxylate reductase, phospho-glycolate phosphatase, and isocitrate dehydrogenase were detected in the cell extracts. The serine formed by Chlorella or Chlamydomonas after 12 seconds of photosynthetic C14O2 fixation contained 70-80% of its C14 in the carboxyl C. This distribution of label in serine was similar to that in phosphoglycerate from the same experiment. Thus, in algae serine is probably formed directly from phosphoglycerate. These results differ from those of higher plants which form uniformly labeled serine from glycolate in short time periods when phosphoglycerate is still carboxyl-labeled. In glycolate formed by algae in 5 and 10 seconds of C14O2 fixation, C2 was at least twice as radioactive as C1. A similar skewed labeling in C2 and C3 of 3-phosphoglycerate and serine suggests a common precursor for glycolate and 3-phosphoglycerate. Glycine formed by the algae from the same experiments, however, was uniformly labeled. Mn-deficient Chlorella incorporated only 2% of the total C14O2 fixed in 10 minutes into glycolate, while in normal Chlorella 30% of the total C14 was found in glycolate. Mn-deficient Chlorella also accumulated more C14 in glycine and serine. Glycolate excretion by Chlorella was maximal in 10 m[image] bicarbonate and occurred only in the light, and was not influenced by the addition of glycolate. No time-dependent uptake of significant amounts of either glycolate or phosphoglycolate was observed. When small amounts of glycolate-2-C14 were fed to Chlorella or Scenedesmus, only 2-3% was metabolized after 30-60 minutes. The algae were not capable of significant glycolate metabolism as is the higher plant. The failure to detect glycolate oxidase, the low level glycolate-Cl4 metabolism, and the formation of serine from phosphoglycerate rather than from glycolate are consistent with the concept of an glycolate pathway in algae.