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The maturation of the inner membrane of foetal rat liver mitochondria.

ABSTRACT: A new method was devised for the isolation of foetal and neonatal rat lvier mitochondria, giving higher yields than conventional methods. 2. During development from the perinatal period to the mature adult, the ratio of cytochrome oxidase/succinate-cytochrome c reductase changes. 3. The inner mitochondrial membrane of foetal liver mitochondria possesses virtually no osmotic activity; the permeability to sucrose decreases with increasing developmental age. 4. Foetal rat liver mitochondria possess only marginal respiratory control and do not maintain Ca2+-induced respiration; they also swell in respiratory-control medium in the absence of substrate. ATP enhances respiratory control and prevents swelling, adenylyl imidodiphosphate, ATP+atractyloside enhance the R.C.I. (respiratory control index), Ca2+-induced respiratory control and prevent swelling, whereas GTP and low concentrations of ADP have none of these actions. It is concluded that the effect of ATP depends on steric interaction with the inner mitochondrial membrane. 5. When 1-day pre-partum foetuses are obtained by Caesarean section and maintained in a Humidicrib for 90 min, mitochondrial maturation is "triggered", so that their R.C.I. is enhanced and no ATP is required to support Ca2+-dependent respiratory control or to inhibit mitochondrial swelling. 6. It is concluded that foetal rat liver mitochondria in utero do not respire, although they are capable of oxidative phosphorylation in spite of their low R.C.I. The different environmental conditions which the neonatal rat encounters ex utero enable the hepatic mitochondria to produce ATP, which interacts with the inner mitochondrial membrane to enhance oxidative phosphorylation by an autocatalytic mechanism.

SUBMITTER: Pollak JK

PROVIDER: S-EPMC1165763 | biostudies-other | 1975 Sep

REPOSITORIES: biostudies-other

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Project description:1. Marker enzymes for the mitochondrial matrix, inner membrane, inter-membrane space and outer membrane were measured in mitochondria isolated from control and regenerating rat liver. The specific activity of these enzymes was then followed for up to 30 days after operation. 2. The specific activity of marker enzymes for the matrix, inner membrane and inter-membrane space remained constant during liver regeneration. 3. However, the specific activities of monoamine oxidase and kynurenine hydroxylase, both outer-membrane markers, fell by 67% and 49% respectively from their control values at 4 days after operation, and returned to normal by about 3 weeks. 4. The repression of kynurenine hydroxylase activity was shown to be unrelated to any independent variation in tryptophan catabolism, based on tryptophan pyrrolase assays. 5. These results are considered to indicate that enzymes of the inner and outer mitochondrial membranes are synthesized asynchronously during morphogenesis. 6. The enzyme complement of purified outer membrane at 4 days after operation was about 50% of that of the appropriate control. Thus the composition of the outer membrane itself may vary dramatically, and supports the concept that constitutive enzymes may turn over independently of a membrane's existence. 7. The behaviour of the rotenone-insensitive, NADH cytochrome c reductase did not parallel the other outer-membrane enzymes for intact mitochondria, but did so when assayed in highly purified fractions of outer membrane. This suggests a labile binding to the outer membrane during the early stages of morphogenesis. 8. Electrophoresis of inner- and outer-membrane proteins revealed little difference between control and experimental mitochondria at 4 days, except for an increase in several, high-molecular-weight components of the outer membrane. These bands closely correspond to similar bands derived from smooth endoplasmic reticulum. 9. The results are discussed in relation to the biogenesis and turnover of mitochondria, and are considered to provide evidence for turnover as a unit, at least for the matrix, inner membrane, inter-membrane space and possibly some form of primary outer membrane.

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The maturation of the inner membrane of foetal rat liver mitochondria.

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