海洋細菌の無機塩要求性に関する生理学的研究-V
細胞質膜のコハク酸酸化における無機塩要求性
1976 年 42 巻 10 号 p. 1115-1120
詳細
1976 年 42 巻 10 号 p. 1115-1120
In order to investigate the mechanism of the type-specific salt requirements for the succinic acid oxidations of M (marine)-, MH(marine halophilic)-, (terrestrial halophilic)-and T (terrestrial)-types, salt requirements for the succinic acid oxidations of the cytoplasmic membrane and cytoplasm were studied with the Warburg respiro-meter. Penicillin-induced spheroplasts of M-, MH-, TH- and T-types were obtained in hypertonic media containing sucrose, MgCl2 and 400 units per ml of penicillin Gas described in the previous paper. Harvested spheroplasts were disrupted in a hypotonic tris-buffer solution (pH 7.4) containing no salt, and washed five times with the same solution. Upon centrifugation, the supernatant was taken as the cytoplasm fraction and the debris was obtained as the cytoplasmic membrane fraction.The activity of the succinic acid oxidation was localized in the cytoplasmic membrane fraction but not in the cytoplasm, the former requiring the following salts for optimum oxidation at 25°C: M-type, CaCl2 5mM+MgCl2 10mM+MgSO4 10mM; MH-type, NaCl 140mM+MgCl2 5mM;TH-type, NaCl 100mM+CaCl2 20mM; T-type, none.The Na+ and K+ requirements which are characteristic of intact cells disappeared completely in the cytoplasmic membrane fraction of M-type, and the K+ requirement also disappeared in the case of the MH- TH- and T-types, respectively. On the other hand, cell membrane fraction (cell wall plus cytoplasmic membrane) prepared from lyzed cells fractionated by sucrose density gradient centrifugation, indicated the same salt requirements as did the cytoplasmic membrane fraction.
The findings regarding salt requirements for the succinic acid oxidation supported three points: first, oxidizing enzymes are localized in the cytoplasmic membrane; second, the type-specific salt requirements of M-, MH-, TH- and T-types are attributed to these oxidizing enzymes; third, Na+ and K+ for M-type, and K+ for the other types play important roles in other physiological processes but not in the oxidation of substrates.
