Coordination of photosynthetic and respiratory metabolism in Chlorella vulgaris UAM 101 in the light

In Chlorella vulgaris UAM 101, the presence of glucose altered the photosynthetic and respiratory metabolism in the light. When glucose was added to the growth medium, an increase in the cellular level of enzymes involved in glucose oxidation, namely glucose‐6‐P dehydrogenase (EC 1.1.1.49) and NAD+‐glyceraldehyde‐3‐P dehydrogenase (EC 1.2.1.12), was observed. Glucose also enhanced respiratory O2 consumption. In addition, CO2 released by glucose oxidation was refixed in photosynthesis. The presence of glucose also affected photosynthesis. Phosphoribulokinase (EC 2.7.1.19) and NADP+‐dependent glyceraldehyde‐3‐P dehydrogenase (EC 1.2.1.13), two regulatory enzymes of the reductive pentose phosphate cycle, were increased by glucose. However, Rubisco (EC 4.1.1.39) activity of these cells was lower than that of autotrophic cells. Despite these alterations, the photosynthetic O2 evolution was not significantly inhibited by glucose. On the other hand, an increase in the cytosolic NADP+‐glyceraldehyde‐3‐P dehydrogenase (EC 1.2.1.9) that is involved in obtaining reducing power for anabolic processes was observed. The CO2 levels in the growth medium did not significantly affect the cellular level of enzymes measured in this work, except those involved in biosynthetic pathways. These data suggest that the effect of glucose on photosynthesis and respiration can be explained by alteration of the cellular level of photosynthetic enzymes and respiratory substrates, respectively.