摘要:

Abstract—A hexokinase has been isolated from brain tissue on Sephadex G‐100 and DEAE cellulose which is similar to yeast enzyme in stimulating the AMP‐aminohydrolase activity of rat brain soluble fractions. This effect of hexokinase is influenced neither byN‐acetyl‐glucosamine nor noradrenaline. An isoenzyme of hexokinase isolated from brain tissue on DEAE cellulose, having properties similar to that of the muscle enzyme, has no effect on AMP‐aminohydrolase activity. The activating effect of yeast hexokinase is not due to its oligomeric structure. Enzyme subunits obtained by the treatment of native yeast enzyme by urea also activate AMP‐aminohydrolase of rat brain solu

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1974.tb04357.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—Rat brain contains the enzyme which forms sulphate conjugates of phenols, phenolsulphotransferase (EC 2.8.2.1), but the physiological role of the enzyme is unclear. The enzyme is unevenly distributed in rat brain, with the activity 13 times higher in the hypothalamus than in the cerebellum. Phenolsulphotransferase does not seem to be primarily located in glial cells. Cultured cells (type C6 astrocytoma) derived from rat glia had less than 1 per cent of the phenolsulphotransferase activity of whole rat brain. Sulphate conjugation of neutral compounds may be important in their removal from brain. The pineal and pituitary glands, areas outside the blood‐brain barrier had very low phenolsulphotransferase activity. The activity of the enzyme in brain varied widely among different species: rabbit and rat had much higher levels of activity than mouse or frog; the activity in human brain was intermediate. Phenolsulphotransferase also occurred in other organs, including liver, heart, testes, lung, spleen, salivary glands, and intact or decentralized superior cervical ganglion. There was no correlation of enzyme activity with adrenergic or cholinergic innervation, or with the known roles of various tissues in drug metabolism or detoxification. The enzyme activity does not seem to be under neuronal control since ganglionectomy did not affect the phenolsulphotransferase activity of salivary glands. The precise localization of phenolsulphotransferase remains to be established, as well as the physiological importance of sulphate conjugation of phenols in brain and other org

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1974.tb04358.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—The oxidation to CO2and the incorporation of [U‐14C]glucose and [U‐14C]acetate into lipids by cortex slices from rat brain during the postnatal period were investigated. The oxidation of [U‐14C]glucose was low in 2‐day‐old rat brain, and increased by about two‐fold during the 2nd and 3rd postnatal weeks. The oxidation of [U‐14C]acetate was increased markedly in the second postnatal week, but decreased to rates observed in 2‐day‐old rat brain at the time of weaning. Both labeled substrates were readily incorporated into non‐saponifiable lipids and fatty acids by brain slices from 2‐day‐old rat. Their rates of incorporation and the days on which maximum rates occurred were different, however, maximum incorporation of [U‐14C]glucose and [U‐14]acetate into lipid fractions being observed on about the 7th and 12th postanatal days, respectively. The metabolic compartmentation in the utilization of these substrates for lipogenesis is suggested. The activities of glucose‐6‐phosphate dehydrogenase, cytosolic NADP‐malate dehydrogenase, cytosolic NADP‐isocitrate dehydrogenase, ATP‐citrate lyase and acetyl CoA carboxylase were measured in rat brain during the postnatal period. All enzymes followed somewhat different courses of development; the activity of acetyl CoA carboxylase was, however, the lowest among other key enzymes in the biosynthetic pathway, and its developmental pattern paralleled closely the fatty acid synthesis from [U‐14C]glucose. It is suggested that acetyl CoA carboxylase is a rate‐limiting step in the synthesisde

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1974.tb04359.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—Injection of a soluble protein fraction from mouse brain into rabbits gave rise to an antibody which was specific for galactocerebroside. The antigen had the following characteristics: (1) it was present in the soluble fraction of a mouse brain homogenate but absent from the soluble fraction of homogenates of mouse liver, spleen, kidney and testis; (2) it was non‐dialysable; (3) it voided from a Sephadex G200 column; (4) on immunodiffusion with antibody directed against it, it gave a sharp single precipitin band; (5) it bound to DEAE cellulose column and was eluted with high salt. Given these characteristics the antigen might have been identified as a ‘brain specific protein’. However, the lipid nature of the antigen was revealed when it was found that it was not destroyed by Pronase digestion and could be quantitatively extracted with chloroform‐methanol. The antigen has been identified as a galaetocerebroside and is 100 times more abundant in the myelin fraction than in the soluble fraction of the mouse brain homogenates. The antigen could have been falsely identified as a ‘brain specific protein’ if the antigenicity and macromolecular behaviour of lipids w

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1974.tb04360.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—The relationships between plasma tryptophan and 5‐HT metabolism in the CNS were studied in newborn rats and compared with adults. Both the concentration of free tryptophan in plasma and that of the amino‐acid in brain were much higher immediately after birth than later on. Drugs such as salicylate and chlordiazepoxide, which increased brain tryptophan concentrations in adults by displacing the plasma amino acid bound to serum albumin, were ineffective in newborn rats: most of the amino acid being already free in their plasma. The study of 5‐HT metabolism in brain stem slices revealed that the affinity of the uptake process for tryptophan was higher in newborn than in adult animals, whereas the reverse situation was observed for the enzyme complex involved in 5‐HT synthesis (lower apparentKmin adults). In addition, the catabolism of newly synthesized 5‐HT was more rapid in newborn than in adult tissues. Finally, the free state of tryptophan in plasma of newborn animals induced in brain both a high amino acid concentration and, in contrast to the situation observed in adults, a synthesis rate of 5‐HT very near its

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1974.tb04361.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—The intracellular localization of phenol sulphotransferase in rat brain was studied The distribution pattern found after differential centrifugation closely resembles that of lactate dehydrogenase and does not change during postnatal development. The distribution of the enzyme in discontinuous and continuous sucrose gradients, however, shows a deviation from the lactate dehydrogenase pattern and a shift towards a higher sucrose concentration during development. In the adult the phenol sulphotransferase coincides with monoamine oxidase, succinate dehydrogenase and β‐glucuronidase. Disruption experiments, purification of mitochondria and electron microscopy exclude localization of phenol sulphotransferase in mitochondria. These studies support the idea of phenol sulphotransferase as a cytoplasmic enzyme with a preferential binding to or localization in oligodendroglial cells or, more probably, a specific type of synaptos

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1974.tb04362.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—Glucose is a major precursor of glutamate and related amino acids in the retina of adult rats.14C from labelled glucose appears to gain access to a large glutamate pool, and the resulting specific activity of glutamate labelled from glucose is always higher than that of glutamine or the other amino acids.Radioactive acetate appeared to label a small glutamate pool. The specific activity of glutamine labelled from acetate relative to that of glutamate was always greater than 1.0. Other precursors of the small glutamate pool were found to include glutamate, aspartate, GABA, serine, leucine and sodium bicarbonate.The level of radioactivity present in retinae incubated with [U‐14C]glucose or [1‐14C]sodium acetate was reduced in the presence of 10−5m‐ouabain. Under these conditions, the relative specific activity of glutamine labelled from [1‐14C]sodium acetate was lowered, but it was raised when [U‐14C]glucose was used as substrate. Ouabain also considerably reduced the synthesis of GABA from [1‐14C]sodium acetate. In all cases ouabain caused a fall in the tissue levels of the amino acids.Aminooxyacetic acid (10−4m) almost completely abolished the labelling of GABA from both [U‐14C]glucose and [1‐14C]sodium acetate, while the RSA of glutamine labelled from the latter substrate was significantly increased. Aminooxyacetic acid raised the tissue concentration of glutamate, but caused a fall in the tissue concentrations of glutamine, aspartate and GABA.The results suggest that there are separate compartments for the metabolism of glutamate in retina and that these can be modified in different wa

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1974.tb04363.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—The presence of rapidly transported axonal proteins in purified preparations of myelin has been investigated in the goldfish visual system. Fish were injected intraocularly with3H proline and contralateral optic tecta were pooled 8–12 h later for purification of myelin. Three purification procedures were employed using continuous and discontinuous gradients of sucrose and continuous gradients of CsCl. All of the myelin preparations were found to have physical, chemical and enzymatic properties attributable to relatively pure preparations of myelin. The goldfish myelin differed from mammalian preparations in having a slightly lower density and in containing an additional major protein of approx. 45,000 mol. wt. All of the myelin preparations retained relatively high levels of axonally transported radioactivity with specific radioactivities which ranged from 70 to 80 per cent of that of the whole tectal homogenate. Acrylamide gel analysis showed the myelin‐associated radioactivity to be confined to the higher molecular weight proteins with very little radioactivity associated with basic protein or proteolipid protein. Both the axonally transported radioactivity and the group of higher molecular weight proteins were found to be more concentrated in a myelin subfraction of relatively high density than in a subfraction of low density. The possible significance of the association of axonally transported proteins with myelin is disc

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1974.tb04364.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—The period during which trans‐synaptic stimulation is required by the rat superior cervical ganglion for induction of tyrosine hydroxylase by reserpine has been studied. Ganglia were decentralized on one side at various times before or after an injection of reserpine. The tyrosine hydroxylase activity of the denervated and control ganglia was assayed 72 h after drug treatment. When decentralization was performed 8 h after an injection of reserpine the increase in tyrosine hydroxylase activity was blocked in the denervated ganglia. Decentralization 12 h after reserpine treatment or later had no effect on the enzyme induction. The actual increase in tyrosine hydroxylase activity occurred between 24 and 48 h after injection of reserp

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1974.tb04365.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—The metabolism of free amino acids: γ‐aminobutyric acid (GABA), glutamine, glycine and glutathione has been studied. The labelling of these free amino acids in normal and in myelin‐deficient brains of Jimpy mice was followed after intraperitoneal injection of14C‐labelled glucose precursor. The quantitative distribution of these amino acids in the two kinds of mouse brain has been compared. A higher level of GABA and a faster labelling of the amino acids in Jimpy than in normal mouse brain was

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1974.tb04366.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY