摘要:

Abstract—Rabbit retinas were maintainedin vitroin medium that resembled CSF but with leucine varied from 2 to 1000μM. Both leucine and threonine were isotopically labelled. When leucine in the medium was 100‐1000μM, leucine was incorporated into protein at 2.03 ± 0.04 (s.E.M.) μmol/g dry wt./h, a turnover per h of 0.55% of the leucine in retinal protein. Incorporation was constant for at least 7 h. It was reduced 34% when the other amino acids were omitted from the medium and 24% when they were increased 15 fold above physiological levels. When medium leucine was reduced to 2 μM with other amino acids constant,14C‐leucine incorporation fell 70%; without significant change in3H‐threonine incorporation, indicating a fall in intracellular specific activity of leucine. The intracellular/extracellular concentration ratio of labelled leucine was 4:1 with medium leucine 23 μM. It fell markedly when medium leucine was reduced to 2 μM or increased to 1000 μM. The concentration ratio of labelled threonine was 15:1 with medium leucine at physiological levels but fell to 6:1 when medium leucine was increased to 1000 μM. Decarboxylation removed 1.5% of free intracellular leucine per min and, at physiological concentrations, was 7.7% the rate of protein incorporation. The ratio of protein synthesis/breakdown, estimated from changes in leucine and 7 other essential amino acids in the medium, was nearly unity. The potential of this preparation for study of CNS protein metabol

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1976.tb00301.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—Unidirectional leucine fluxes were measured in isolated rabbit retina maintained under steady state conditions in medium resembling CSF but with leucine varied from 2 to 20,000 μM. At physiological leucine concentration (11 μM), 1/2 time for outward transport was 88 s and intracellular fluid was cleared of Isotopically labelled leucine at 2.3ml/g dry wt./min; 1/2 time for inward transport was 16 s and interstitial fluid was cleared at 7.5 ml/g dry wt./min. The rate of leucine influx corresponded quite well with its rate of disappearance from the intracellular fluid, over a wide range of concentrations. Exchange diffusion was demonstrated for transport in both directions. There was competition by other amino acids, but no interaction between Na+and leucine transport could be demonstrated. Kinetic analysis indicated the presence of more than one transport system for leucine. There was an unexpected fall in the efflux coefficient, with reduction in leucine concentration at the lower end of the concentration range, for which an explanation is proposed. Under control conditions, 1/2 time for efflux of intracellular24Na+was about 0.9 min. With intracellular Na+increased 4 fold, l/2 time for efflux was slightly reduced. Problems encountered in measuring fluxes in organized tissue are discus

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1976.tb00302.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—Data on leucine metabolism in isolated rabbit retina are examined for evidence, for or against, a common intracellular pool of free leucine. Data include values for: concentrations, transport rates, degradative metabolism and protein incorporation of labelled leucine measured over a wide range of concentrations; protein incorporation of labelled threonine, measured simultaneously; and an indirect measurement of protein breakdown. The fall in labelled leucine incorporation into protein, when medium leucine was reduced below 100 μM, corresponded closely with the fall in intracellular specific activity predicted from rate of influx of labelled leucine from medium and rate of release of unlabelled leucine from protein breakdown. Protein incorporation of labelled leucine competed with decarboxylation and outward transport and reduced the free intracellular leucine in about the amounts predicted for a common pool. Implications for measurements using labelled amino acid are discuss

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1976.tb00303.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—Non‐ionic detergents stimulated particulate guanylate cyclase activity in cerebral cortex of rat 8‐ to 12‐fold while stimulation of soluble enzyme was 1.3‐ to 2.5‐fold. Among various detergents, Lubrol PX was the most effective one. The subcellular distribution of guanylate cyclase activity was examined with or without 0.5% Lubrol PX. Without Lubrol PX two‐thirds of the enzyme activity was detected in the soluble fraction. In the presence of Lubrol PX, however, two‐thirds of guanylate cyclase activity was recovered in the crude mitochondrial fraction. Further fractionation revealed that most of the particulate guanylate cyclase activity was associated with synaptosomes. The sedimentation characteristic of the particulate guanylate cyclase activity was very close to those of choline acetyltransferase and acetylcholine esterase activities, two synaptosomal enzymes. When the crude mitochondrial fraction was subfractionated after osmotic shock, most of guanylate cyclase activity as assayed in the absence of Lubrol PX was released into the soluble fraction while the rest of the enzyme activity was tightly bound to synaptic membrane fractions. The total guanylate cyclase activity recovered in the synaptosomal soluble fraction was 6 to 7 times higher than that of the starting material. The specific enzyme activity reached more than 1000 pmol per min per mg protein, which was 35‐fold higher than that of the starting material. The membrane bound guanylate cyclase activity was markedly stimulated by Lubrol PX. Guanylate cyclase activity in the synaptosomal soluble fraction, in contrast, was suppressed by the addition of Lubrol PX. The observation that most of guanylate cyclase activity was detected in synaptosomes, some of which was tightly bound to the synaptic membrane fraction upon hypoosmotic treatment, is consistent with the concept that cyclic GMP is involved in ne

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1976.tb00304.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

AbstractIt had been proposed that sialyl‐residues on the surface of the cell control the activity of certain plasma membrane ecto‐enzymes. We have tested the effects of several established (or presumptive) ecto‐enzymes in tissue cultures of CNS‐derived cells.Application of neuraminidases to cultured mouse neuroblastoma (N‐18), neonatal Syrian hamster astrocytes (NN), human astrocytoma (Cox clone) and two lines of primary mouse astroblasts failed to change the activity of ecto‐ATPase and 5′‐nucleotidase. Only two of the seven neuraminidase preparations produced marked or moderate increases in inorganic pyrophosphatase,p‐nitrophenylphosphatase and cholinesterase. We have concluded that the stimulation of these enzymes was not due to removal of sialyl‐residues. We suggest that contaminants (haemolysins?) in neuraminidase preparations ofClostridium perfringensincreased membrane permeability and facilitated substrate‐

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1976.tb00305.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—The effects of insulin‐induced hypoglycemic stupor and subsequent treatment with glucose on mouse cerebral cortical, cerebellar and brain stem levels of glucose, glycogen, ATP, phosphocreatine, glutamate, aspartate and GABA and on cerebral cortical and cerebellar levels of cyclic AMP and cyclic GMP have been measured. Hypoglycemia decreased glucose, glycogen and glutamate levels and had no effect on ATP levels in all three regions of brain. GABA levels were decreased only in cerebellum. Aspartate levels rose in cerebral cortex and brain stem, and creatine phosphate increased in cerebral cortex and cerebellum. In the hypoglycemic stuporous animals, cyclic GMP levels were elevated in cerebral cortex and depressed in cerebellum whereas cyclic AMP levels were unchanged from control values. Intravenous administration of 2.5–3.5 mmol/kg of glucose to the hypoglycemic stuporous animals produced recovery of near normal neurological function within 45 s. Only brain glucose and aspartate levels returned to normal prior to behavioral recovery. These results suggest that of the several substances examined in this study, only glucose and perhaps aspartate have important roles in the biochemical mechanisms producing neurological abnormalities in hypoglycemic an

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1976.tb00306.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—The phospholipid composition as well as thein vivo[14C]glycerol uptake in lipids was found to be similar in the toad brain and retina. The choroid lipid labeling was markedly different. Anin vitrotime‐course study of [14C]glycerol incorporation in toad retina lipids disclosed that under the conditions of these experiments: (1) retina is able to rapidly synthetize phosphatidic acid from the radioactive precursor; (2) the sequence phosphatidic acid‐diacylglycerol‐triacylglycerol operates; (3) a high rate of phosphatidylinositolde novobiosynthesis takes place; (4) phosphoglycerides of choline and of ethanolamine are also heavily labeled after a lag period; (5)in vivolabeling profiles resembled those obtainedin vitromainly regarding phosphatidylinositol biosynthesis; and (6) the presence of glycerol kinase in the CNS is su

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1976.tb00307.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—Rat mouse AChE molecular forms are indistinguishable with respect to their sedimentation coefficients and their evolutive proportions during brain maturation. Among rat or mouse erythrocytes, rat C6glial cells, and mouse 2A and NS 20 neuroblastoma cells, only neuroblastoma cells showed both the ES and HS molecular forms with a 1:1 proportion for NS 20 cells. All these cells lack a third molecular form (16S), which is present in rat and mouse superior cervical ganglia. After irreversible inhibition of pre‐existing NS 20 neuroblastoma AchE, the ES form is first synthesized (de novosynthesis). The HS form begins to appear after a lag time of several hours and represents, 24 h after inhibition, only 15% of the total recovered activity, which is near the initial level. The initial relative proportions return by 2 to 3 days after inhibition. The recovery of the HS form is, for the most part, blocked by actinomycin D, which does not block the recovery of activity itself, which remains as an ES form.It seems that integration of the ES form into the HS form more probably depends on the synthesis of a new messenger RNA, which is required for the synthesis of either new AChE polypeptide chain, polymerization initiating protein or activating enz

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1976.tb00308.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—The kinetic parameters of monoamine oxidase (MAO; E.C 1.4.3.4) and catechol‐O‐methyl‐transferase (COMT; EC 2.1.1.6) were evaluated in extracts of adrenergic and non‐adrenergic mouse neuroblastoma cells and in rat glioma cells. Using the naturally‐occurring substrates tyramine, tryptamine, serotonin and norepinephrine, the affinity of MAO for a given substrate was independent of the presence of the catecholaminergic pathway or cell type used, with apparentKmvalues ranging from 8–14 μM for tryptamine to 510–580 μM for norepinephrine. The MAO activity in glioma cells was substantially greater than in either neuroblastoma clone, butVmaxvalues varied little with substrate among cell lines. Both the neuronal and glial COMT had a similarKmfor I‐norepinephrine (200μM); the correspondingVmaxvalues were also similar among the different cell lines, but represented only 2–10% of the maximal MAO activity. Neuroblastoma and glioma cells, when grown from early logarithmic to stationary phase, showed no significant changes in specific activity of either MAO or COMT. Growth of cells for 3 days with 1 mM‐N6,O2′‐dibutyryl adenosine‐3′,5′‐cyclic monophosphate resulted in no marked change in either MAO or COMT activity.These results suggest that in neurons neither MAO nor COMT plays a major role in the type of transmitter inactivation that is analogous to that of acetylcholinesterase in cholinergic synapses. The occurrence of considerable MAO and acetylcholinesterase activities in glioma cells may indicate a role for these ce

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1976.tb00309.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—The lipid composition of the brain, including myelin, was studied in detail in two cases with a variant form of metachromatic leukodystrophy (multiple sulphatase deficiency type).In the white matter, the sulphatide concentration was 3–4 times higher than the normal level in both cases. There was a significant accumulation of cholesterol sulphate in the brain, liver and kidney of both cases. The ganglioside pattern in the grey and white matter was abnormal, with a higher proportion of GM3, GM2and GD3‐gangliosides. Non‐lipid hexosamine contents were increased 1.5‐2 times in brain, 8–10 times in liver and 2–3 times in kidney. Increased amounts of glucocerobroside, ceramide lactoside and ceramide trihexoside were present in grey and white matter of both cases.Recovery of purified myelin from two patients’brains was much less than from control (1–20% in case 1 and 20–30% in case 2). The lipid composition of myelin was almost normal except for a higher proportion of sulphatide, with a decreased amount of cerebroside. The fatty acid compositions of myelin sulphatide and sphingomyelin were almost normal, while non‐hydroxy fatty acids of cerebroside contained less long‐chain fatty acids, as characterized by a significant increase of C16:0 and C18:0 fatty acids. The myelin polypeptide pattern by SDS‐disc gel electrophoresis showed a relative decrease of basic protein and of proteolipid protein.A possible mechanism of myelin

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1976.tb00310.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY