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PubMed1965

THE STIMULATION BY TREATMENT IN VIVO WITH TRI-IODOTHYRONINE OF AMINO ACID INCORPORATION INTO PROTEIN BY ISOLATED RAT-LIVER MITOCHONDRIA.

1. Normal and thyroidectomized rats were treated with near-physiological doses of tri-iodothyronine. Liver mitochondria were isolated and incubated with radioactive amino acids. In normal rats tri-iodothyronine caused only a slight stimulation of incorporation into mitochondrial protein, but in thyroidectomized animals the incorporation was doubled. 2. There was a lag period of about 36 hr. after injection and the maximum effect was observed after 2 days. 3. Direct addition of tri-iodothyronine to the incubation medium had no effect on mitochondrial incorporation. 4. The incorporation was not due to bacterial, nuclear, lysosomal or microsomal contamination and the labelled particles had sedimentation properties identical with those of mitochondria, as followed by suitable enzyme markers. 5. Thyroid hormone treatment did not cause any marked alterations in the pattern of labelling of submitochondrial fractions and in all cases the most radioactive protein was in an insoluble lipid-rich fraction. The amino acid compositions of the total mitochondrial protein and the more radioactive lipoprotein were also unaltered. 6. Increases in the content of RNA and various cytochromes per mg. of mitochondrial protein were observed after treatment with tri-iodothyronine. These occurred slightly later than the stimulation of amino acid incorporation. 7. No uncoupling of oxidative phosphorylation was observed and the ATP production per mg. of mitochondrial protein increased. 8. It was concluded that tri-iodothyronine stimulated amino acid incorporation into mitochondrial protein and that the result is consistent with the view that treatment with thyroid hormone results in an enhanced selective synthesis of mitochondrial respiratory units.

Acid Phosphatase↗

PubMed1965

SOME FEATURES OF MITOCHONDRIA AND FLUFFY LAYER IN REGENERATING RAT LIVER.

1. Mitochondria and fluffy layer were prepared from control and regenerating rat liver. Differential and density-gradient centrifugation were used to fractionate the preparations, which were examined for protein content, density and the activity of cytochrome c oxidase, succinate dehydrogenase, NAD-isocitrate dehydrogenase and NADP-isocitrate dehydrogenase. 2. During regeneration the mitochondrial protein content of the liver fell by 18% from the control value of 18.4mg. of protein/g. of liver (wet wt.) and by 3 weeks had risen to 130% of the control value. It then declined slowly. 3. The fluffy-layer protein content (4.7mg./g. of liver) varied inversely as the mitochondrial content and increased by 70% in the early stages (10 days) of liver regeneration. The results suggest that fluffy layer may partially represent both partly formed and broken-down mitochondria. 4. NAD- and NADP-isocitrate dehydrogenases differed in their behaviour during liver regeneration. 5. The succinate-dehydrogenase and NADP-isocitrate-dehydrogenase activity of fluffy layer was high and rose during the early stages of liver regeneration (1 week). Succinate dehydrogenase and cytochrome c oxidase were concentrated in the lighter fluffy-layer particles 10 days to 3 weeks after partial hepatectomy. The significance of this with respect to mitochondrial formation is discussed. 6. Mitochondrial fractions possessed a certain degree of heterogeneity in enzymic activity when separated according to size and density. The mean density of heavy mitochondria was 1.198, light mitochondria 1.193. Fluffy layer was nearly homogeneous in control liver, but during regeneration considerable heterogeneity became evident. The significance of the heterogeneity is discussed.

Chemistry Techniques, Analytical↗

PubMed1965

CARBOHYDRATE METABOLISM IN LIVER FROM FOETAL AND NEONATAL SHEEP.

1. During development of the sheep, the activities of UDP-glucose-alpha-glucan glucosyltransferase and UDP-glucose pyrophosphorylase and the glycogen content are highest in the liver of lambs 2 weeks old and considerably lower in liver from adult sheep. 2. The activity of hexokinase and the rate of incorporation of [(14)C]-glucose into glycogen are much lower in liver from postnatal sheep than in rat liver. 3. The activities of hexose diphosphatase and glucose 6-phosphatase and the rates of incorporation of [(14)C]pyruvate and [(14)C]propionate into glycogen increase from low levels in the liver of foetal sheep to maxima a few weeks after birth. The activities in the liver of adult sheep are slightly lower. 4. The incorporation rate of [(14)C]pyruvate into glucose has been measured in liver slices from rats, sheep and chick embryos at several ages of these animals. This pathway is active in liver from foetal sheep, embryonic chicks and postnatal rats or sheep, but is absent from the liver from foetal rats. 5. Fructose metabolism, as measured by the rates of incorporation of [(14)C]fructose into glycogen and glucose in liver slices and by assays of liver ketohexokinase, is barely detectable in the liver of foetal sheep and appears soon after birth. 6. During development of the sheep, the incorporation rate of [(14)C]galactose into glycogen in liver slices is highest in foetal sheep and decreases with increasing age of the animal. 7. These findings are discussed with reference to the changing pattern of carbohydrate metabolism during neonatal development of liver in the sheep.

Animals↗

PubMed1965

RAT-KIDNEY LYSOSOMES: ISOLATION AND PROPERTIES.

1. The activities of lysosomal enzymes in the cortexes and medullas and the principal subcellular fractions of rat kidney were measured. 2. A method is described for the isolation of rat-kidney lysosomes and a detailed analysis of the enzymic composition of the lysosomes is reported. Enzyme analysis of the other principal subcellular fractions is included for comparison. 3. Studies of the distribution of alpha-glucosidase showed that the lysosomal fraction contained only 10% of the total enzyme activity. The microsomal fraction contained most of the particulate alpha-glucosidase. Lysozyme was concentrated mainly in the lysosomal fraction with only small amounts present in the microsomal fraction. Lysosomal alpha-glucosidase had optimum pH5 whereas the microsomal form had optimum pH6. Both lysosomal and microsomal lysozyme had optimum pH6.2. 4. The stability of lysosomal suspensions was studied. Incubation at 37 degrees and pH7 resulted in first an increased availability of enzymes without parallel release of enzyme. This was followed by a second stage during which the availability of enzymes was closely related to the release of enzymes. These changes were closely paralleled by changes in light-scattering properties of lysosomes. 5. The latent nature of the alpha-glucosidase and lysozyme of intact kidney lysosomes was demonstrated by their graded and parallel release with other typical lysosomal enzymes. 6. Isolated lysosomes were unstable at pH values lower than 5, most stable at pH6-7 and less stable at pH 8-9. Lysosomes were not disrupted when the osmolarity of the suspending medium was decreased from 0.6m to 0.25m. 7. The discussion compares the properties and composition of kidney lysosomes, liver lysosomes and the granules of macrophages. 8. The possible origin of the lysozyme in kidney lysosomes by reabsorption of the lysozyme in blood is discussed.

Acid Phosphatase↗

PubMed1965

STUDIES ON THE TISSUE ACTIVATOR OF PLASMINOGEN. DISTRIBUTION OF ACTIVATOR AND PROTEOLYTIC ACTIVITY IN THE SUBCELLULAR FRACTIONS OF RABBIT KIDNEY.

1. On subcellular fractionation of rabbit kidney by differential and density-gradient centrifugation, a high proportion of the tissue activator of plasminogen activity was found to be particulate and displayed sedimentation properties associated with the lysosome-rich fraction as judged biochemically by the acid-phosphatase activity. 2. The activator activity is closely associated with a latent protease whose activity is enhanced in the presence of Triton X-100 or sodium deoxycholate in the neutral pH range. Besides hydrolysing casein this protease is also capable of attacking fibrinogen at pH7.4. 3. The pH optimum for activator activity and its inhibition by in-hexanoic acid (in-aminocaproic acid) point to its possible similarity to urokinase, an activator of plasminogen present in the urine of most mammals.

Acid Phosphatase↗

PubMed1965

THE ISOLATION AND CHARACTERIZATION OF SUBCELLULAR COMPONENTS OF THE EPITHELIAL CELLS OF RABBIT SMALL INTESTINE.

1. Homogenization of the epithelial cells of rabbit small intestine in 0.3m-sucrose-5mm-EDTA, pH7.4, maintains intact the microvillus sheets that form the lumenal surface of the cells, the nuclei, the mitochondria and the vesicles (microsomes) formed from the endoplasmic reticulum. 2. These particulate components of the cell, and the cell-sap fraction, have been isolated by differential centrifuging of cell homogenates. 3. The nuclei and microvillus sheets sediment together and it has been impossible to separate these subcellular components by centrifugal methods. 4. The isolated subcellular fractions have been identified by a combination of light-microscopic examination, electron-microscopic examination, chemical analysis and assay for selected enzyme activities.

Acid Phosphatase↗

PubMed1965