Modes of proton translocation across the cell membrane of respiring cyanobacteria

Acidification of weakly buffered suspensions of the cyanobacteria Anacystis nidulans, Nostoc sp. strain MAC, Dermocarpa sp. and Anabaena variabilis was observed after the application of oxygen pulses to anaerobic cells. The acidification was caused by proton extrusion from the oxygen pulsed cells since it was eliminated by the uncoupler (H⁺ ionophore) carbonyl cyanide m-chlorophenylhydrazone. Results with the inhibitors dicyclohexylcarbodiimide or 7-chloro-4-nitrobenz-2-oxa-1,3-diazole, orthovanadate and cyanide indicated the association of various fractions of the observed proton extrusion with different activities of the cell membrane, viz. a H⁺-translocating reversible F₀F₁-ATPase, a unidirectional H⁺-translocating ATP hydrolase, and a respiratory electron transport system, respectively. Further parameters investigated were the pH dependence and the H⁺/O stoichiometry of the H⁺ extrusion from oxygen pulsed cyanobacteria. H⁺/O ratios at neutral pH were between 4 (Anacystis nidulans) and 0.3 (Dermocarpa) with uninhibited, actively phosphorylating cells and between 2 (Anacystis nidulans) and 0.4 (Dermocarpa) with ATPase-inhibited (ATP-depleted) cells, respectively. It is significant that with all four cyanobacteria tested a major fraction of the observed H⁺ ejection remained unaffected by ATPase inhibitors even at concentration which completely abolished all oxidative phosphorylation. Vanadate had a major effect on the H⁺ extrusion from Anabaena only. From this it is concluded that in the cyanobacterial species investigated part of the H⁺ extrusion from oxygen pulsed cells is directly linked to some H⁺-translocating respiratory electron transport chain present in the cell membrane.Abbreviations CCCP carbonyl cyanide m-chlorophenylhydrazone - DCCD N, N-dicyclohexylcarbodiimide - DCMU N-(3,4-dichlorophenyl-)N,N-dimethylurea - NBD 7-chloro-4-nitrobenzoxa-1,3-diazole - TPP⁺ tetraphenylphosphonium - Mes 2-(N-morpholino)ethanesulfonic acid - Pipes piperazine-N,N-bis-(2-ethanesulfonic acid) - Hepes N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - Taps tris (hydroxymethyl)-methyl-aminopropanesulfonic acid - Ches 2-(N-cyclohexylamino)-ethanesulfonic acid - Caps 3-cyclohexylamino)-1-propanesulfonic acid; according to most textbooks (e.g. Nicholls 1982) the terms proton electrochemical potential () and protonmotive force (pmf, p), both of which equivalently describe the energetic state of energy-transducing membranes, were used synonymously and expressed in mV units throughout this article (however, cf. Lowe and Jones 1984)Dedicated to Prof. G. Drews on the occasion of his 60th birthday