Abstract
It has been reported that the mitochondrial cytochromes and citrate cycle enzymes occur in constant proportions to each other and increase or decrease roughly in parallel in response to various stimuli. The purpose of this study was to determine whether this proportionality is an obligatory consequence of the way in which mitochondria are assembled. Severe iron deficiency was used to bring about decreases of the iron-containing constituents of the mitochondrial respiratory chain in skeletal muscle. Cytochrome c concentration and cytochrome oxidase activity were decreased approximately 50%, while succinate dehydrogenase and NADH dehydrogenase activities were decreased by 78% in iron-deficient muscle. On electron microscopic examination, mitochondria in iron-deficient muscles had relatively sparse numbers of cristae. The iron deficiency had little or no effect on the levels of a range of mitochondrial matrix enzymes, including citrate synthase, isocitrate dehydrogenase, fumarase, aspartate aminotransferase, 3-hydroxyacyl-CoA dehydrogenase, 3-ketoacid-CoA transferase, and acetoacetyl-CoA thiolase. These results show that the usual constant proportions between the constituents of the mitochondrial respiratory chain and matrix enzymes are not obligatory; they provide evidence that mitochondrial matrix enzymes and respiratory chain constituents can be incorporated into mitochondria independently and that the ratios between them can vary within wide limits.
Highlights
It has been reported that the mitochondrial cyto- to tissue respiratory capacity and content of respiratory enchromes and citrate cycle enzymes occur in constant zymes, and it has been estimated that the citrate synthase proportions to each other and increase or decrease content of mitochondria of differenttissues alsovaries in roughly in parallel in response to various stimuli
These results show that the usual con- In this context, we undertook the present study to deterstant proportions between the constituents of the mi- mine whether a large change in the concentrations of comtochondrial respiratory chain and matrix enzymes are ponents of the respiratory chain results in parallel changes in not obligatory; they provide evidence that mitochon- enzymes of the mitochondrial matrixA.s a toolwe used severe drial matrix enzymes and respiratory chain constitu- iron deficiency, which has been shown to cause a large deents canbe incorporated into mitochondria independ- crease in the iron-containing components of the respiratory ently and that the ratios betweenthem can vary within wide limits
Cytochrome oxidase and succinate dehydrogenase activities were measured on whole musclehomogenates, cytochrome c concentration was determined on an extract of whole muscle,and NADH dehydrogenase activity was measured on the mitochondrial fraction prepared by fractional extraction
Summary
Louis-Jacques Cartier$, Yoshinobu Ohira, May Chen, RobertW. Cuddiheeg, and John 0.Holloszy. These results show that the usual con- In this context, we undertook the present study to deterstant proportions between the constituents of the mi- mine whether a large change in the concentrations of comtochondrial respiratory chain and matrix enzymes are ponents of the respiratory chain results in parallel changes in not obligatory; they provide evidence that mitochon- enzymes of the mitochondrial matrixA.s a toolwe used severe drial matrix enzymes and respiratory chain constitu- iron deficiency, which has been shown to cause a large deents canbe incorporated into mitochondria independ- crease in the iron-containing components of the respiratory ently and that the ratios betweenthem can vary within wide limits
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