Glycolaldehyde Inhibits CO(2) Fixation in the Cyanobacterium Synechococcus UTEX 625 without Inhibiting the Accumulation of Inorganic Carbon or the Associated Quenching of Chlorophyll a Fluorescence.

When studying active CO(2) and HCO(3) (-) transport by cyanobacteria, it is often useful to be able to inhibit concomitant CO(2) fixation. We have found that glycolaldehyde was an efficient inhibitor of photosynthetic CO(2) fixation in Synechococcus UTEX 625. Glycolaldehyde did not inhibit inorganic carbon accumulation due to either active CO(2) or HCO(3) (-) transport. When glycolaldehyde (10 millimolar) was added to rapidly photosynthesizing cells, CO(2) fixation was stopped within 15 seconds. The quenching of chlorophyll a fluorescence remained high (</= 82% control) when CO(2) fixation was completely blocked by glycolaldehyde. This quenching was relieved upon the addition of a glucose oxidase oxygentrap. This is consistent with our previous finding that q-quenching in the absence of CO(2) fixation was due to O(2) photoreduction. Photosynthetic CO(2) fixation was also inhibited by d,l,-glyceraldehyde but a sixfold higher concentration was required. Glycolaldehyde acted much more rapidly than iodoacetamide (15 seconds versus 300 seconds) and did not cause the onset of net O(2) evolution often observed with iodoacetamide. Glycolaldehyde will be a useful inhibitor when it is required to study CO(2) and HCO(3) (-) transport without the complication of concomitant CO(2) fixation.