Kinetics of Glucose Incorporation by Aphanocapsa 6714

Abstract

Photoautotrophic metabolism of CO 2 was compared with glucose metabolism in the facultative unicellular blue-green alga, Aphanocapsa 6714. Glucose-fed cells incorporated more 14 C into phosphorylated sugar intermediates of the reductive and oxidative pentose phosphate cycles than autotrophic cells. The relative increases were: 140-fold in dark cells; 32-fold in dichlorophenylmethylurea (DCMU)-inhibited cells; and 16-fold in cells assumilating glucose during photosynthetic carbon reduction. On the other hand, incorporation of 14 C from glucose into 3-phosphoglycerate and the amino acid pools of glutamate and aspartate was reduced in dark cells. Rates of protein synthesis in dark and DCMU-inhibited cells were reduced 50 and 80% compared to photoautotrophic cells. In cells assimilating glucose during photosynthesis, rates of 14 C incorporation into the two amino acids and protein were the same as in photoautotrophic cells. Chase experiments, using an excess of 12 C-glucose and CO 2 , revealed slow turnover of carbon in dark cells and intermediate turnover rates in DCMU-inhibited cells, when compared to cells assimilating glucose during photosynthesis.