ジギトニン処理permeable腹水肉腫細胞におけるミトコンドリアの酸化的リン酸化

ラウス肉腫ウィルス誘発腹水肉腫細胞(SR-C3H/He)を低濃度のジギトニン(終末0.01%)で処理し,基質透過性細胞とすることにより,少量の材料で簡単にミトコンドリアの呼吸速度,呼吸調節率(RCR),酸化的リン酸化能(ADP/0 比)などの機能を酸素電極法を用いて調べられることがわかった.この基質透過性腹水肉腫細胞ではマウス肝や腹水肉腫細胞から分離したミトコンドリアより,呼吸調節率や酸化的リン酸化能が幾分低い.この原因について種々なATPase活性を検討した結果,この透過性細胞では主にミトコンドリア以外のMg(2+)-ATPase活性がかなり高く存在し,これによって呼吸調節率や酸化的リン酸化能の低下が生じることが示唆された.また,この透過性細胞に解糖系の基質であるグルコースやホスホエノールピルビン酸を添加しhexokinaseやpyruvate kinaseの存在による呼吸調節への影響を認めたが,解糖系の一連の反応は不連続であり,呼吸調節率や酸化的リン酸化能の低下の主因であるとは考え難い.このように,低濃度のジギトニン処理透過性細胞は比較的少量のwhole cellでのミトコンドリアの酸化的リン酸化と呼吸阻害剤や脱共役剤の影響を簡便に調べることができ,さらに細胞内オルガネラの機能と代謝系の相関をin vivoに近い条件下で調べることのできるきわめて有用な実験系であると考えられる.

Substrate-permeable cells were prepared by treatment of Rous Sarcoma virus-induced mouse ascites sarcoma cells (SR-C3H/He) with a low concentration of digitonin. Using relatively small amounts of the digitonin-treated permeable cells, mitochondrial functions such as a respiratory rate, respiratory control ratio (RCR), and ADP/O ratio of oxidative phosphorylation were easily measured by the oxygen electrode method. The permeable ascites sarcoma cell mitochondria had a slightly lower RCR and ADP/O ratio than mitochondria isolated from mouse liver and ascites sarcoma cells. This result was found to be mainly due to higher extramitochondrial Mg(2+)-ATPase activity in the permeable ascites sarcoma cells. The effects of hexokinase and pyruvate kinase on the RCR and the ADP/O ratio were investigated by the additions of glucose and phosphoenolpyruvate as substrates, but these enzymes can not be the main factors in decreasing the RCR and the ADP/O ratio in the permeable ascites sarcoma cells since the glycolytic pathway was not continuous in these cells. The digitonin-treated permeable cell system is an extremely useful system for studying mitochondrial functions and their relations to other organelae and metabolic pathways under near in vivo conditions.