Bicarbonate uptake in the marine macroalga Ulva sp. is inhibited by classical probes of anion exchange by red blood cells

We demonstrate in this work that HCO_inf3^sup-uptake in the marine macroalga Ulva sp. features functional resemblances to anion transport mediated by anion exchangers of mammalian cell membranes. The evidence is based on (i) competitive inhibition of photosynthesis by the classical red-blood-cell anion-exchange blockers 4,4′-dinitrostilbene-2,2′-disulfonate and 4-nitro-4′-isothiocyanostilbene-2,2′-disulfonate under conditions where HCO_inf3^sup-, but not CO₂, was the inorganic carbon form taken up; (ii) inhibition of HCO_inf3^-uptake by pyridoxal phospate, indicating the involvement of lysine residues in the binding/translocation of HCO_inf3^sup-; and (iii) inhibition of HCO_inf3^sup-(but not of CO₂) uptake by exofacial trypsin treatments, indicating the functional involvement of a plasmalemma protein. It is suggested that HCO_inf3^sup-uptake mediated by such a putative anion transporter can be a fundamental step in providing inorganic carbon for the CO₂-concentrating system of marine marcoalgae in an environment where the HCO_inf3^sup-concentration is high, but the CO₂ concentration and rates of uncatalyzed HCO_inf3^sup-dehydration are low.