Trchounian A, Ohanjanyan Y, Bagramyan K, Vardanian V, Zakharyan E, Vassilian A, Davtian M
Department of Biophysics, Biological Faculty of the Yerevan State University, Armenia.
Biosci Rep. 1998 Jun;18(3):143-54. doi: 10.1023/a:1020144628839.
K+ uptake by the Escherichia coli TrkA system is unusual in that it requires both ATP and deltamuH+; a relation with H+ circulation through the membrane is therefore suggested. The relationship of this system with the F0F1-ATPase was studied in intact cells grown under different conditions. A significant increase of the N,N'-dicyclohexylcarbodiimide(DCCD)-inhibited H+ efflux through the F0F1 by 5 mM K+, but not by Na+ added into the potassium-free medium was revealed only in fermenting wild-type or parent cells, that were grown under anaerobic conditions without anaerobic or aerobic respiration and with the production of H2. Such an increase disappeared in the deltaunc or the trkA mutants that have altered F0F1 or defective TrkA, respectively. This finding indicates a closed relationship between TrkA and F0F1, with these transport systems being associated in a single mechanism that functions as an ATP-driven H(+)-K(+)-exchanging pump. A DCCD-inhibited H(+)-L(+)-exchange through these systems with the fixed stoichiometry of H+ and K+ fluxes (2H+/K+) and a higher K+ gradient between the cytoplasm and the external medium were also found in these bacteria. They were not observed in cells cultured under anaerobic conditions in the presence of nitrate or under aerobic conditions with respiration and without production of H2. The role of anaerobic or aerobic respiration as a determinant of the relationship of the TrkA with the F0F1 is postulated. Moreover, an increase of DCCD-inhibited H+ efflux by added K+, as well as the characteristics of DCCD-sensitive H(+)-K(+)-exchange found in a parent strain, were lost in the arcA mutant with a defective Arc system, suggesting a repression of enzymes in respiratory pathways. In addition, K+ influx in the latest mutant was not markedly changed by valinomycin or with temperature. The arcA gene product or the Arc system is proposed to be implicated in the regulation of the relationship between TrkA and F0F1.
大肠杆菌TrkA系统对钾离子的摄取不同寻常，因为它既需要ATP又需要质子动力势（ΔμH⁺）；因此表明其与质子通过膜的循环有关。在不同条件下生长的完整细胞中研究了该系统与F0F1 - ATP酶的关系。仅在厌氧条件下生长且无厌氧或有氧呼吸并产生氢气的发酵野生型或亲本细胞中，发现5 mM钾离子可使通过F0F1的N，N'-二环己基碳二亚胺（DCCD）抑制的质子外流显著增加，而在无钾培养基中添加钠离子则无此作用。这种增加在分别具有改变的F0F1或缺陷型TrkA的Δunc或trkA突变体中消失。这一发现表明TrkA与F0F1之间存在紧密关系，这些转运系统以单一机制相关联，该机制起ATP驱动的H⁺-K⁺交换泵的作用。在这些细菌中还发现，通过这些系统以固定的H⁺和K⁺通量化学计量比（2H⁺/K⁺）进行的DCCD抑制的H⁺-L⁺交换以及细胞质与外部介质之间更高的K⁺梯度。在硝酸盐存在下厌氧培养或有氧呼吸且不产生氢气的条件下培养的细胞中未观察到这些现象。推测厌氧或有氧呼吸作为TrkA与F0F1关系的决定因素的作用。此外，在具有缺陷型Arc系统的arcA突变体中，添加钾离子导致的DCCD抑制的质子外流增加以及在亲本菌株中发现的DCCD敏感的H⁺-K⁺交换特性丧失，这表明呼吸途径中的酶受到抑制。此外，缬氨霉素或温度对最新突变体中的钾离子内流没有明显影响。有人提出arcA基因产物或Arc系统参与调节TrkA与F0F1之间的关系。
