Sekler I, Gläser H U, Pick U
Department of Biochemistry, Weizmann Institute of Science, Israel.
J Membr Biol. 1991 Apr;121(1):51-7. doi: 10.1007/BF01870650.
Dunaliella acidophila is an unicellular green alga which grows optimally at pH 0-1 while maintaining neutral internal pH. A plasma membrane preparation of this algae has been purified on sucrose density gradients. The preparation exhibits vanadate-sensitive ATPase activity of 2 mumol Pi/mg protein/min, an activity 15 to 30-fold higher than that in the related neutrophilic species D. salina. The following properties suggest that the ATPase is an electrogenic plasma membrane H+ pump. (i) ATP induces proton uptake and generates a positive-inside membrane potential as demonstrated with optical probes. (ii) ATP hydrolysis and proton uptake are inhibited by vanadate, diethylstilbestrol, dicyclohexylcarbodiimide and erythrosine but not by molybdate, azide or nitrate. (iii) ATP hydrolysis and proton uptake are stimulated by fussicoccin in a pH-dependent manner as found for plants plasma membrane H(+)-ATPase. Unusual properties of this enzyme are: (i) the Km for ATP is around 60 microM, considerably lower than in other plasma membrane H(+)-ATPases, and (ii) the ATPase activity and proton uptake are stimulated three to fourfold by K+ and to a smaller extent by other monovalent cations. These results suggest that D. acidophila possesses a vanadate-sensitive H(+)-ATPase with unusual features enabling it to maintain the large transmembrane pH gradient.
嗜酸杜氏藻是一种单细胞绿藻，在pH值为0 - 1时生长最佳，同时能维持细胞内pH值中性。这种藻类的质膜制剂已通过蔗糖密度梯度进行了纯化。该制剂表现出对钒酸盐敏感的ATP酶活性，为2 μmol无机磷/毫克蛋白/分钟，这一活性比相关的嗜中性物种盐生杜氏藻高15至30倍。以下特性表明该ATP酶是一种生电质膜H⁺泵。（i）ATP诱导质子摄取并产生膜内正电位，这已通过光学探针得到证实。（ii）ATP水解和质子摄取受到钒酸盐、己烯雌酚、二环己基碳二亚胺和赤藓红的抑制，但不受钼酸盐、叠氮化物或硝酸盐的抑制。（iii）如在植物质膜H⁺ - ATP酶中所发现的，ATP水解和质子摄取受到壳梭孢菌素以pH依赖方式的刺激。该酶的异常特性为：（i）ATP的米氏常数约为60 μM，远低于其他质膜H⁺ - ATP酶；（ii）ATP酶活性和质子摄取受到K⁺的刺激，提高三到四倍，受到其他单价阳离子的刺激程度较小。这些结果表明嗜酸杜氏藻拥有一种具有异常特征的对钒酸盐敏感的H⁺ - ATP酶，使其能够维持较大的跨膜pH梯度。
