Hess J L, Tolbert N E
Plant Physiol. 1967 Mar;42(3):371-9. doi: 10.1104/pp.42.3.371.
No glycolate oxidase activity could be detected by manometric, isotopic, or spectrophotometric techniques in cell extracts from 5 strains of algae grown in the light with CO(2). However, NADH:glyoxylate reductase, phosphoglycolate phosphatase and isocitrate dehydrogenase were detected in the cell extracts. The serine formed by Chlorella or Chlamydomonas after 12 seconds of photosynthetic (14)CO(2) fixation contained 70 to 80% of its (14)C in the carboxyl carbon. 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 (14)CO(2) fixation, C(2) was at least twice as radioactive as C(1). A similar skewed labeling in C(2) and C(3) of 3-phosphoglycerate and serine suggests a common precursor for glycolate and 3-phosphoglycerate. Glycine formed by the algae, however, from the same experiments was uniformly labeled. Manganese deficient Chlorella incorporated only 2% of the total (14)CO(2) fixed in 10 minutes into glycolate, while in normal Chlorella 30% of the total (14)C was found in glycolate. Manganese deficient Chlorella also accumulated more (14)C in glycine and serine.Glycolate excretion by Chlorella was maximal in 10 mm 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-(14)C were fed to Chlorella or Scenedesmus, only 2 to 3% was metabolized after 30 to 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-(14)C metabolism, and the formation of serine from phosphoglycerate rather than from glycolate are consistent with the concept of an incomplete glycolate pathway in algae.
采用测压法、同位素法或分光光度法，在5种在光照及CO₂条件下培养的藻类细胞提取物中均未检测到乙醇酸氧化酶活性。然而，在细胞提取物中检测到了NADH：乙醛酸还原酶、磷酸乙醇酸磷酸酶和异柠檬酸脱氢酶。小球藻或衣藻在光合固定(¹⁴)CO₂ 12秒后形成的丝氨酸，其羧基碳中的(¹⁴)C含量占70%至80%。丝氨酸中这种标记分布与同一实验中磷酸甘油酸的标记分布相似。因此，在藻类中，丝氨酸可能直接由磷酸甘油酸形成。这些结果与高等植物不同，高等植物在短时间内从乙醇酸形成均匀标记的丝氨酸，而此时磷酸甘油酸仍带有羧基标记。在藻类光合固定(¹⁴)CO₂ 5秒和10秒时形成的乙醇酸中，C₂的放射性至少是C₁的两倍。3-磷酸甘油酸和丝氨酸的C₂和C₃中类似的偏向性标记表明乙醇酸和3-磷酸甘油酸有共同的前体。然而，在相同实验中藻类形成的甘氨酸是均匀标记的。缺锰的小球藻在10分钟内固定的总(¹⁴)CO₂中，只有2%掺入到乙醇酸中，而正常小球藻中30%的总(¹⁴)C存在于乙醇酸中。缺锰的小球藻在甘氨酸和丝氨酸中也积累了更多的(¹⁴)C。小球藻在10 mM碳酸氢盐中乙醇酸排泄量最大，且仅在光照下发生，并且不受乙醇酸添加的影响。未观察到对乙醇酸或磷酸乙醇酸有明显的随时间的摄取。当向小球藻或栅藻投喂少量的乙醇酸-2-(¹⁴)C时，30至60分钟后只有2%至3%被代谢。藻类不像高等植物那样能够进行显著的乙醇酸代谢。未检测到乙醇酸氧化酶、低水平的乙醇酸-(¹⁴)C代谢以及从磷酸甘油酸而非乙醇酸形成丝氨酸，这些都与藻类中乙醇酸途径不完整的概念一致。
