Phosphatidate biosynthesis in mitochondrial subfractions of rat liver

1. After conventional fractionation of rat liver homogenates in 0·88m-sucrose the mitochondrial fraction was subjected to short-term water lysis followed by separation of the resulting membrane preparations. 2. Phosphatidate formation was measured in all subcellular fractions and subfractions and was compared with the distribution of succinate dehydrogenase, monoamine oxidase, rotenone-insensitive NADH cytochrome c reductase, arylsulphatase, urate oxidase, arylesterase and glucose 6-phosphatase. 3. The results obtained indicated that mitochondria were capable of synthesizing phosphatidate, though this activity was only about one-third of the total homogenate activity. 4. Mitochondrial phosphatidate formation was located predominantly in the outer mitochondrial membrane. Although this membrane preparation was found to be significantly contaminated by the microsomal fraction, this contamination was estimated to account for not more than about 20% of the total phosphatidate formation observed in preparations of outer mitochondrial membrane.

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Enzymatically inactive forms of acetyl-CoA carboxylase in rat liver mitochondria

Biochemical Journal ◽

10.1042/bj2510881 ◽

1988 ◽

Vol 251 (3) ◽

pp. 881-885 ◽

Cited By ~ 6

Author(s):

J B Allred ◽

C R Roman-Lopez

Keyword(s):

Rat Liver ◽

Microsomal Fraction ◽

Specific Activity ◽

Polyacrylamide Gel Electrophoresis ◽

Mitochondrial Fraction ◽

Liver Mitochondria ◽

Rat Liver Mitochondria ◽

Outer Mitochondrial Membrane ◽

Acetyl Coa Carboxylase ◽

Acetyl Coa

Biotinyl proteins were labelled by incubation of SDS-denatured preparations of subcellular fractions of rat liver with [14C]methylavidin before polyacrylamide-gel electrophoresis. Fluorographic analysis showed that mitochondria contained two forms of acetyl-CoA carboxylase [acetyl-CoA:carbon dioxide ligase (ADP-forming) EC 6.4.1.2], both of which were precipitated by antibody to the enzyme. When both forms were considered, almost three-quarters of the total liver acetyl-CoA carboxylase was found in the mitochondrial fraction of liver from fed rats while only 3.5% was associated with the microsomal fraction. The remainder was present in cytosol, either as the intact active enzyme or as a degradation product. The actual specific activity of the cytosolic enzyme was approx. 2 units/mg of acetyl-CoA carboxylase protein while that of the mitochondrial enzyme was about 20-fold lower, indicating that mitochondrial acetyl-CoA carboxylase was relatively inactive. Fractionation of mitochondria with digitonin showed that acetyl-CoA carboxylase was associated with the outer mitochondrial membrane. The available evidence suggests that mitochondrial acetyl-CoA carboxylase represents a reservoir of enzyme which can be released and activated under lipogenic conditions.

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Glucose metabolism in cancer cells: immunogold localization of hexokinase to the outer mitochondrial membrane

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100141597 ◽

1995 ◽

Vol 53 ◽

pp. 1044-1045

Author(s):

Krishan K. Arora ◽

Glenn L. Decker ◽

Peter L. Pedersen

Keyword(s):

Tumor Cells ◽

Mitochondrial Membrane ◽

Present Report ◽

Large Fraction ◽

Mitochondrial Fraction ◽

Immunogold Labeling ◽

Outer Mitochondrial Membrane ◽

Immunogold Localization ◽

Hexokinase Activity ◽

Normal Tissues

Hexokinase (ATP: D-hexose 6-phophotransferase EC 2.7.1.1) is the first enzyme of the glycolytic pathway which commits glucose to catabolism by catalyzing the phosphorylation of glucose with ATP. Previous studies have shown diat hexokinase activity is markedly elevated in rapidly growing tumor cells exhibiting high glucose catabolic rates. A large fraction (50-80%) of this enzyme activity is bound to the mitochondrial fraction (1,2) where it has preferred access to ATP (3). In contrast,the hexokinase activity of normal tissues is quite low, with one exception being brain which is a glucose-utilizing tissue (4). Biochemical evidence involving rigorous subfractionation studies have revealed striking differences between the subcellular distribution of hexokinase in normal and tumor cells [See review by Arora et al (4)].In the present report, we have utilized immunogold labeling techniques to evaluate die subcellular localization of hexokinase in highly glycolytic AS-30D hepatoma cells and in the tissue of its origin, i.e., rat liver.

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