Intracellular pH Regulation in an Acidophilic Unicellular Alga, Cyanidium caldarium: 31P-NMR Determination of Intracellular pH |
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Authors: | Enami, Isao Akutsu, Hideo Kyogoku, Yoshimasa |
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Affiliation: | 1Department of Biology, Faculty of Science, Science University of Tokyo Kagurazaka, Shinjuku-ku, Tokyo 162, Japan 2Department of Physical Chemistry, Faculty of Engineering, Yokohama National University Tokiwadai, Hodogaya-ku, Yokohama 240, Japan 3Institute for Protein Research, Osaka University Suita, Osaka 565, Japan |
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Abstract: | The intracellular pH of an acidophilic unicellular alga, Cyanidiumcaldarium, was determined as a function of external pH by 31Pnuclear magnetic resonance. The algal cells incubated underaerobic conditions or under anaerobic and illuminated conditionsmaintained the intracellular pH in the range from 6.8 to 7.0even when the external pH was changed from 1.2 to 8.4. Underanaerobic and dark conditions, however, the intracellular pHacidified at the acidic pH region of the external medium. Theacidified intracellular pH reversibly returned to neutral eitheron aeration or illumination. The results indicate that, in Cyanidiumcells growing in extremely acidic environments, an active H+efflux (H+ pump) which depends on metabolic activity (respirationor photosynthesis) is essential to maintain the intracellularpH at a constant physiological level against the passive H+leakage due to the steep pH gradient across the cell membrane. (Received March 19, 1986; Accepted July 17, 1986) |
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