Coenzyme Q-pool function in glycerol-3-phosphate oxidation in hamster brown adipose tissue mitochondria |
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Authors: | Hana Rauchová Maurizio Battino Romana Fato Giorgio Lenaz Zdeněk Drahota |
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Institution: | (1) Institute of Physiology, Czechoslovak Academy of Sciences, Prague, Czechoslovakia;(2) Institute of Biochemistry, University of Ancona, Italy;(3) Department of Biochemistry, University of Bologna, Italy |
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Abstract: | We have investigated the role of the Coenzyme Q pool in glycerol-3-phosphate oxidation in hamster brown adipose tissue mitochondria. Antimycin A and myxothiazol inhibit glycerol-3-phosphate cytochromec oxidoreductase in a sigmoidal fashion, indicating that CoQ behaves as a homogeneous pool between glycerol-3-phosphate dehydrogenase and complex III. The inhibition of ubiquinol cytochromec reductase is linear at low concentrations of both inhibitors, indicating that sigmoidicity of antimycin A and myxothiazol inhibition is not a direct property of antimycin A and myxothiazol binding. Glycerol-3-phosphate cytochromec oxidoreductase is strongly stimulated by added CoQ3, indicating that endogenous CoQ is not saturating. Application of the pool equation for nonsaturating ubiquinone allows calculation of theK
m for endogenous CoQ of glycerol-3-phosphate dehydrogenase of 3.14mM. The results of this investigations reveal that CoQ behaves as a homogeneous pool between glycerol-3-phosphate dehydrogenase and complex III in brown adipose tissue mitochondria; moreover, its concentration is far below saturation for maximal electron transfer activity in comparison with other branches of the respiratory chain connected with the CoQ pool. HPLC analysis revealed a lower amount of CoQ in brown adipose mitochondria (0.752 nmol/mg protein) in comparison with mitochondria from other tissues and the presence of both CoQ9 and CoQ10. |
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Keywords: | Glycerol-3-phosphate dehydrogenase coenzyme Q-pool ubiquinol cytochromec reductase brown adipose tissue mitochondria |
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