Ethoxyzolamide Inhibition of CO₂ Uptake in the Cyanobacterium Synechococcus PCC7942 without Apparent Inhibition of Internal Carbonic Anhydrase Activity

Abstract

In high inorganic carbon grown (1% CO2 [volume/volume] There is now mounting evidence that cyanobacteria grown under high Cj2 conditions (1% CO2) possess a CO2 utilizing C1 pump which forms the central component of the CO2 concentrating mechanism (3, 5). The C1 pump appears to be constitutively expressed, being apparent even in 1 % CO2 grown cells (5). It has been proposed that induction of the high affinity HCO-uptake system during growth at low C1 levels may be due to the addition ofa "front-end" mechanism that converts HCO3 to CO2 with CO2 then feeding into the C1 pump (3,5).Although the Ci pump in high Ci grown cells appears to utilize CO2 as substrate (5,20), various arguments and evidence suggest that HCO03 is the species that arrives inside the cell (2,3,25).

Selective and Reversible Inhibition of Active CO2 Transport by Hydrogen Sulfide in a Cyanobacterium

“…Previous studies have suggested the participation ofa membrane-bound CA-like moiety in the transport of CO2 by Anabaena variabilis, Anacystis nidulans R2, and Synechococcus PCC 7942 (1,22,25,28). This conclusion was largely based on the observation that EZ inhibited CO2 transport (1,22,25,28) without apparent inhibition of intracellular CA (25).…”

“…This conclusion was largely based on the observation that EZ inhibited CO2 transport (1,22,25,28) without apparent inhibition of intracellular CA (25). Inhibition of CO2 transport by H2S in Synechococcus UTEX 625 further strengthens the view that CA and the CO2 transport system have properties in common.…”

“…This model differs from previous models (1,22,25,28) in that the CO2 and HCO3-transport systems are considered to be separate, specific, and independent. As discussed here and elsewhere (7,8,13,19) evidence for this arrangement is provided primarily from studies with selective inhibitors.…”

“…In Synechococcus PCC 7942, however, it has been proposed that HCO3F from the medium is converted to CO2 within the membrane by a 'front end mechanism' and that this CO2 is then used as a substrate for the CO2 transport system (4,25). Both the CO2 delivered by the front end mechanism and CO2 taken up directly from the medium are converted to HC03-by a CA-like function of the CO2 transport system during passage across the membrane (25). Thus, in the former case CO2 uptake is obligately dependent upon a HC03-transport system while, in the latter case, HCO3-uptake is obligately dependent upon a CO2 transport system.…”

Utilization of inorganic carbon in the edible cyanobacterium Ge‐Xian‐Mi (Nostoc) and its role in alleviating photo‐inhibition

“…This was due to the inhibition of Na + -dependent HCO 3 -transport by the presence of Li + ions (Espie, Miller & Canvin 1988). Because the membrane-permeable carbonic anhydrase inhibitor EZ inhibited the CO 2 -uptake systems (Price & Badger 1989), the net photosynthetic activity was 70% of control with the addition of 25 mmol L -1 NaCl + 300 mmol L -1 EZ (Fig. 2).…”