Ramírez J, Peña A, Montero-Lomelí M
Department of Microbiology, Universidad Nacional Autónoma de México, Mexico.
Biochim Biophys Acta. 1996 Dec 4;1285(2):175-82. doi: 10.1016/s0005-2736(96)00153-8.
The activity of a putative H+/K+ exchange system in the plasma membrane of yeast was studied following the alkalinization of the interior of vesicles prepared with lecithin and yeast plasma membrane containing pyranine entrapped inside. The fluorescence of pyranine was used as an indicator of the internal pH of the vesicles. The addition of monovalent cations produced an increase of the internal pH, probably due to the activity of an exchange system, allowing H+ to leave the vesicle in an exchange for the cation added. The system showed partial selectivity towards K+ against other monovalent cations, and it was inhibited by amiloride. The activity of this system required the presence of the yeast plasma membrane in the vesicles, and it did not produce important changes of the membrane potential of the vesicles. The exchange depended partially on the relative values of the internal and the external pH of the vesicles. The system shows low affinity for the cations, and appears to be different from the mitochondrial H+/K+ exchange system, which is non-selective toward the different monovalent cations. This system could be involved in the regulation of the internal pH of the cells when they accumulate high concentrations of K+.
利用包裹有吡喃荧光素的卵磷脂和酵母质膜制备囊泡，在囊泡内部碱化后，对酵母质膜中假定的H⁺/K⁺交换系统的活性进行了研究。吡喃荧光素的荧光用作囊泡内部pH值的指示剂。单价阳离子的加入使内部pH值升高，这可能是由于交换系统的活性，使得H⁺离开囊泡以交换加入的阳离子。该系统对K⁺相对于其他单价阳离子表现出部分选择性，并且被氨氯吡脒抑制。该系统的活性需要囊泡中存在酵母质膜，并且它不会使囊泡的膜电位产生重要变化。这种交换部分取决于囊泡内部和外部pH值的相对值。该系统对阳离子的亲和力较低，并且似乎不同于线粒体H⁺/K⁺交换系统，后者对不同单价阳离子无选择性。当细胞积累高浓度K⁺时，该系统可能参与细胞内部pH值的调节。
