bluuebunny/crossref_metadata_2025_split huggingface dataset:
CHARACTERIZATION OF MEMBRANES OBTAINED FROM ELECTRIC ORGAN OF THE ELECTRIC EEL BY SUCROSE GRADIENT FRACTIONATION AND BY MICRODISSECTION
Authors: Rosenberg P. , Silman I. , Ben‐David E. , de Vries A. , Condrea E. 
Published: October 2006

Abstract— Two membrane fractions were obtained from electric organ tissue of the electric eel by sucrose gradient centrifugation of tissue homogenates. Electron microscopic examination showed that both fractions contained mainly vesicular structures (microsacs). Both the light and heavy fractions had a‐bungarotoxin‐binding capacity and Na+‐K+ ATPase activity, while only the light fraction had AChE activity. The polypeptide patterns of vesicles derived from both the light and heavy fractions were examined by SDS‐polyacrylamide gel electrophoresis and found to be very similar. The ratio of protein to phospholipid in the light vesicles was much lower than in the heavy vesicles, but the relative amounts of individual phospholipids in the two fractions were similar.A marked difference in the permeability of the light and heavy vesicles was observed by measuring efflux of both [14C]sucrose and 22Na+, and also by monitoring volume changes induced by changing the osmotic strength of the medium. All three methods showed the heavy vesicles to be much more permeable than the light ones. Only the light vesicles displayed increased sodium efflux in the presence of carbamylcholine.The AChE in the light fraction does not appear to be membrane‐bound, but is rather a soluble enzyme, detached from the membrane during homogenization, which migrates on the gradient similarly to that of the light vesicles. This is supported by the fact that the bulk of the AChE is readily removed by washing the vesicles. Moreover, under the conditions employed in our sucrose gradient separations,‘native’14 S + 18 S AChE exists in the form of aggregates which migrate very similarly to the major peak of AChE activity of tissue homogenates.Separated innervated and non‐innervated surfaces of isolated electroplax were obtained by microdissection. α‐Bungarotoxin‐binding capacity was observed only in the innervated membrane. About 80% of the AChE was in the innervated membrane, and about 70% of the Na+‐K+ ATPase in the non‐innervated membrane.The data presented indicate that the light and heavy vesicle fractions separated by sucrose gradient centrifugation are not derived exclusively from the innervated and non‐innervated membranes respectively, as previously suggested by others, but contain membrane fragments from both sides of the electroplax. The separation of two populations on sucrose gradients may be explained both by the differences in permeability and in protein to phospholipid ratios.
PEROXIDASES IN THE NEURAL RETINA AND PIGMENT EPITHELIUM1
Authors: Armstrong D. , Connole E. , Feeney L. , Berman E. R. 
Published: October 2006

AbstractPeroxidase activity, assayed with 2 mM‐H2O2 and suitable hydrogen donors (either p‐phenyl‐enediamine or diaminobenzidine), was demonstrated in homogenates of neural retina and pigment epithelium of both the dog and the cow. The enzyme is particle‐associated in the native state, but is readily extractable by brief sonication or freeze‐thawing. At optimum pH, which is between 4.0 and 4.5 for both sources, the specific activity is up to 40 times greater in pigment epithelial cells than in neural retina. Some catalase activity was detected in extracts from both bovine and canine neural retina, but catalase was essentially absent in pigment epithelium.Fractionation of bovine pigment epithelial cells showed that peroxidase activity is associated mainly with heavy organelles sedimenting at low centrifugal forces. Melanosomes, nuclei, melanolysosomes and plasma membranes were the principal organelles identified in these low speed sediments. It was not possible to separate them either by differential centrifugation or on discontinuous sucrose gradients. However, melanosomes were excluded as the only source of peroxidase activity by isolating separately the melanotic and amelanotic cell populations; equal peroxidase was found in both cell types. Since nuclei are not a likely source of this enzyme, it is suggested that most of the peroxidase activity in bovine pigment epithelial cells is localized in either the melanolysosomes, plasma membranes, or both.
TURNOVER OF PHOSPHATIDYLCHOLINE IN MICROSOMES AND MYELIN IN BRAINS OF YOUNG AND ADULT RATS
Authors: Miller Sheldon L. , Morell Pierre 
Published: October 2006

AbstractWe have tested the hypothesis that the turnover of phosphatidylcholine in subcellular fractions of rat brain is a function of the age at which this lipid is deposited. Rats, 60 days of age, were injected intracranially with [2‐3H]glycerol and either [methyl‐14C]choline (to label the base moiety) or [U‐14C]glucose (to label acyl moieties). Littermates were killed up to 90 days after injection and brain microsomes and myelin isolated. Lipids were extracted and the phosphatidylcholine was isolated by 2‐dimensional TLC and hydrolyzed to its constituent moieties. The 3H in the glycerol backbone and 14C in the choline or acyl residues was quantitated. The microsomal and myelin 3H/14C ratios decreased with time with either set of precursors, indicating that labeled choline and acyl moieties were reutilized more efficiently than the glycerol backbone. The various precursors exhibited first order decay curves with half‐lives for the glycerol backbone of 6 and 11 days for the microsomal and myelin fractions respectively.These results contrast with those previously obtained with identical experimental procedures when 17‐day‐old animals were injected. In that study, although much of the phosphatidylcholine turned over rapidly as for the older animals, by 2 weeks after injection most of the remaining phosphatidylcholine was turning over more slowly with a half‐life of 13 and 25 days for microsomes and myelin respectively (Miller et al., 1977). The base and acyl moieties also had a corresponding shorter half‐life in older animals relative to the slow turnover phase in younger rats.
A CHOLESTEROL‐ESTERIFYING ENZYME IN RAT CENTRAL NERVOUS SYSTEM MYELIN1
Authors: Choi Myung‐Un , Suzuki Kunihiko 
Published: October 2006

AbstractAontrary to our earlier finding (Eto & Suzuki, 1971), the myelin fraction purified from young adult rat brain consistently showed cholesterol‐esterifying activity. The specific activity in myelin was the highest among subcellular fractions. Extensive washing wiih various aqueous salt solutions failed to remove the activity from myelin. The enzyme was evenly distributed among the arbitrarily defined light, medium and heavy myelin subfractions. The myelin‐localized activity showed the pH optimum and heat stability identical to the microsome‐bound activity. Although there were minor differences in the effect of detergents or exogenous lipids added to the reaction mixture, no firm evidence was obtained to indicate that the myelin‐bound cholesterol‐esterifying enzyme is different from that in other subcellular fractions. On the other hand, the distribution among the myelin subfractions and heat stability of the myelin‐bound cholesterol‐esterifying activity were different from those of the myelin‐specific cholesterol ester hydrolase. Therefore, the esterification does not appear to be a mere reverse reaction catalyzed by the previously known myelin‐specific hydrolase. The rat brain myelin, therefore, is capable of both synthesizing and hydrolyzing cholesterol esters.
ACYL GROUP COMPOSITION OF METABOLICALLY ACTIVE LIPIDS IN BRAIN: VARIANCES AMONG SUBCELLULAR FRACTIONS AND DURING POSTNATAL DEVELOPMENT
Authors: Su Kwei Lee , Sun Grace Y. 
Published: October 2006

AbstractUsing a combination of preparative TLC and GLC technique, the content and acyl group composition of diacyl‐glycerophosphoinositols, diacyl‐glycerophosphates, diacylglycerols and triacyl‐glycerols in brain tissue were determined. The level of diacyl‐glycerophosphoinositols in 40 day‐old mouse brain was 2.7 μmol/g tissue as compared to 40–170 nmol/g for other minor lipids. The acyl groups of diacyl‐glycerophosphoinositols were enriched in 18:0 and 20:4 (n‐6). This characteristic acyl group profile was found in microsomes, synaptosomes, and in myelin. The acyl groups of diacyl‐glycerophosphates and diacylglycerols were comprised mainly of 16:0, 18:0, 18:1 and 20:4 (n‐6). In rat brain subcellular fractions, the acyl groups of diacylglycerols and diacyl‐glycerophosphates in the microsomal fraction had a higher proportion of 22:6 (n‐3) than those in the myelin and synaptosomal fractions. The acyl groups of the myelin lipids were higher in 18:l and lower in 20:4 (n‐6) as compared to those in the microsomal and synaptosomal fractions. The triacylglycerols in brain exhibited an unusual acyl group profile which included small proportions of 14:0, 16:1, 20:4 (n‐6), 22:4 (n‐6) and 22:6 (n‐3). Except for an increase in 18:1 and a corresponding decrease in 16:0 which was found in diacyl‐glycerophosphoinositols, no apparent acyl group change was observed in other metabolically active lipids during postnatal brain development.
THE TOXIC EFFECT OF SODIUM GLUTAMATE AND DL‐α‐AMINOADIPIC ACID ON RAT RETINA: CHANGES IN HIGH AFFINITY UPTAKE OF PUTATIVE TRANSMITTERS
Authors: Karlsen R. Lund 
Published: October 2006

AbstractSubcutaneous administration of high doses of sodium glutamate to new born rats was used to destroy retinal interneurons and ganglion cells. Such treatment was accompanied by 90% reduction in the high affinity uptake of choline, 60–70% reductions in the uptakes of GABA, diamino‐n‐butyric acid and glycine and 30–40% reductions in the uptakes of asparatate and glutamate measured on retinal homogenates from 30‐day‐old rats. The high affinity uptakes of β‐alanine and taurine were unchanged. Preincubation of retinal homogenates with 1 mM β‐alanine or 100 μM diamino‐n‐butyric acid severely reduced the high affinity GABA uptake in control and experimental animals.In intact retinae, however, the glutamate treatment increased the high affinity uptake of β‐alanine by 70%, whereas that of diamino‐n‐butyric acid was reduced by 40% and the high affinity uptakes of GABA and glutamate were unchanged.Four hours after injection of the gliotoxic compound DL‐α‐aminoadipic acid into the vitreous body of 30‐day‐old rats, the Müller cells could no longer be identified. This lesion was accompanied by 55% reduction in the high affinity uptake of β‐alanine and 25% reduction in the uptakes of GABA and glutamate on intact retinae. The high affinity uptakes of diamino‐n‐butyric acid, choline and the enzyme activities of choline acetyltransferase and glutamate decarboxylase were unchanged under these conditions. After 24 h, however, the Müller cells could be recognized again, and the β‐alanine uptake had normalized.
STUDIES ON THE TRANSPORT OF GLUTAMINE IN VIVO BETWEEN THE BRAIN AND BLOOD IN THE RESTING STATE AND DURING AFFERENT ELECTRICAL STIMULATION
Authors: Abdul‐Ghani A.‐S. , Marton M. , Dobkin J. 
Published: October 2006

Abstract— In this work we have studied the effect of afferent electrical stimulation (AES) of the contralateral brachial plexus on the release of glutamine and glutamate from the cat's brain into the cerebral venous blood, at rest and during continuous infusion of L‐glutamine and sucrose solutions.(1) In the resting state, before stimulation, there was a net outflow of glutamine from the brain into the cerebral venous blood, but no release of glutamic acid. (2) AES caused release of glutamate and increased 3.5‐fold the release of glutamine. The increase in release of glutamine and glutamate was found to be reversed very shortly after stimulation. (3) Steady intravenous infusion of a 0.3 M‐gluta‐mine solution for 10 min changed the negative arterio‐venous difference in glutamine to a positive one and increased the content in brain by 15×20%. In this case AES caused a singificant drop, to zero of the glutamine arterio‐venous difference. (4) At the onset of pentamethylenetetrazole (PTZ) seizures, like AES, there was a significant reduction of the level of glutamine in the cats’cerebral cortex. This reduction vanished when the animals were infused with L‐glutamine solution but not with 0.3 M‐sucrose solution that was used as an inert electrolyte. (5) The kinetic behaviour of the glutamine transport is compatible with a carrier‐mediated process, but not with passive diffusion.
ENZYMATIC BIOSYNTHESIS OF ETHANOLAMINE‐ AND CHOLINE‐PHOSPHOGLYCERIDES IN RETINA DURING DEVELOPMENT. EFFECT OF LIGHT STIMULATION
Authors: Dreyfus H. , Harth S. , Urban P. F. , Mandel P. , Freysz L. 
Published: October 2006

AbstractCholine‐ and ethanolamine‐phosphoglycerides (CPG and EPG) are the most abundant phospholipids of retinal membranes. We have investigated some regulatory mechanisms involved in the final steps of their biosynthesis, namely those catalysed by CDP‐choline 1,2 diradyl‐sn‐glycerol choline phosphotransferase (CPT) and CDP‐ethanolamine 1,2 diradyl‐sn‐glycerol ethanolamine phosphotransferase (EPT). We have studied both enzymes in the retina which offers an excellent model for the investigation of the molecular basis of the effect of its physiological stimulus, the light. In chick retina. the specific activity (SA) of EPT reached a maximum at the 18th day of embryonic life and decreased thereafter. In the case of CPT, a similar peak of SA was observed at hatching. The time of maximum SA of EPT and CPT corresponded to the period during which retinal rod outer segments are formed. The apparent Km values of EPT and CPT determined with whole retinal homogenates for CDP‐bases showed different profiles. The apparent Km of EPT decreased during embryonic life and increased thereafter whereas the apparent Km of CPT did not change during ontogenesis. Light stimulation of calf retinal homogenates had different effects on phosphotransferase activities. In the presence of only endogenous diacylglycerol (DAG) the SA of CPT was 2‐fold higher for dark‐adapted retinas, whereas no differences in EPT activities were observed. After addition of exogenous DAG (4mM) to the incubation medium, light stimulation of the retina led to a 50% increase of EPT activity whereas no effect was observed for CPT. These different effects could be related to the cyclic nucleotides present in retina before and after light stimulation. In addition all the data presented in this study indicate that, as in brain, CPT and EPT in retina are two different enzymes.
UPTAKE, RELEASE AND HOMO‐ AND HETERO‐EXCHANGE DIFFUSIONS OF INHIBITORY AMINO ACIDS IN GUINEA‐PIG CEREBELLAR SLICES
Authors: Okamoto Koichi , Namima Misako 
Published: October 2006

Abstract— GABA, taurine and β‐alanine are taken up by guinea‐pig cerebellar slices by both the high‐and low‐affinity uptake processes, whereas glycine is taken up only by the low‐affinity process. A considerable amount of labelled GABA loaded in the slice is released by unlabelled external GABA and a minute amount is released by external β‐alanine, glycine and taurine. External glycine and β‐alanine releases labelled glycine loaded in the slice. Labelled taurine loaded is effectively released by external taurine and β‐alanine, while labelled β‐alanine loaded is released only by external β‐alanine.It is suggested that hetero‐exchanges which are one‐directional in some cases also take place between the amino acids in addition to homo‐exchanges. Therefore, high‐affinity uptake processes observed with GABA and taurine could be the result of the homo‐exchange diffusions, while that of β‐alanine could be due to either the homo‐exchange or the hetero‐exchange diffusions or both.K+′‐evoked releases of GABA and to a lesser extent, taurine are partially dependent upon the presence of Ca+ in the superfusion media, whereas that of glycine and probably that of β‐alanine, are not, K+ ‐evoked releases of labelled GABA and taurine are larger when loaded by their high‐affinity uptake systems than by their low‐affinity uptake processes. The reverse is the case with labelled glycine and β‐alanine. These results do not rule out the possibility that taurine might act as a neurotransmitter in the cerebellum.
CHARACTERIZATION OF THE ENZYMIC TRANSFER OF ARACHIDONOYL GROUPS TO 1‐ACYL‐PHOSPHOGLYCERIDES IN MOUSE SYNAPTOSOME FRACTION
Authors: Corbin D. R. , Sun G. Y. 
Published: October 2006

Abstract—In the presence of ATP, Mg2+ and CoA, mouse brain synaptosomes actively catalyze the transfer of arachidonate to 1‐acyl‐phosphoglycerides. The enzymic acylation process was inhibited greatly by 0.1 mm‐PCMB (parachloromercuric benzoate), and only partially by 0.1 mm‐DNP (2,4‐dini‐trophenol) and 0.001% (w/v) oligomycin. Arachidonoyl transfer to 1‐acyl‐glycerophosphorylcholines and 1‐acyl‐glycerophosphorylinositols was negligibly affected by 1 mm‐NaF and 10 mm‐glucose. Among the different 1‐acyl‐phosphoglycerides used as acceptor molecules, the relative order for arachidonoyl transfer activity was: 1‐acyl‐glycerophosphorylinositols > 1‐acyl‐glycerophosphorylcholines > l‐acyl‐glycerophosphorylethanolamines. The ester linkage at the C‐1 position of the 1‐acyl‐phosphoglycerides also appears necessary for activity for no arachidonoyl transfer activity was observed when 1‐alkenyl‐glycerophosphorylethanolamines were used as the acceptor molecules. Arachidonate transfer to 1‐acyl‐glycerophosphorylinositols was optimal at low acceptor concentrations (10–30 μm) whereas the transfer to 1‐acyl‐glycerophosphorylcholines occurred over a much broader range of acceptor concentrations (30–80 μm). At optimal acceptor concentration, maximal transfer activity was observed at arachidonate concentration of 50–80 μm. The newly synthesized phosphoglycerides were found distributed in the subsynaptic components with specific activity highest in the fraction containing synaptic vesicles.
INCORPORATION OF LIPIDS INTO SUBCELLULAR FRACTIONS OF BRAIN OF QUAKING MUTANT
Authors: Albers‐Jackson B. , Greenfield S. , Brostoffand S. W. , Hogan E. L. 
Published: October 2006

Abstract—The synthesis of lipids and their assembly into subcellular membrane fractions of the myelin deficient Quaking mutant and control brains was studied in 18‐, 24‐ and 41‐day‐old animals using a double label methodology with14C and 3H acetate as precursors. As a general procedure, Quaking mutants were injected intracranially with 50 μCi [14C]acetate and their littermate controls with 300 μCi [3H]acetate. The animals were killed 3 h post‐injection, their brains were pooled and subcellular fractions prepared from the common homogenate. An 80‐90% decrease in the incorporation of acetate into eleven lipids of myelin in the Quaking mutant was found. This occurred in the face of apparent normal incorporation (relative to microsomes) into lipids of the other main subcellular fractions (nuclear. mitochondrial and synaptosomal) with the exception of decreased incorporation into the myelin‐like fraction at 18 and 24 days. Cholesterol and cerebroside were less readily incorporated into Quaking myelin than the other lipids. Although the microsomal synthesis of cholesterol and cerebroside was depressed by about 30% in the Quaking mutant, the incorporation of cholesterol into nuclear, synaptosomal and mitochondrial fractions was unaffected in the mutant. This indicates that sufficient cholesterol is synthesized for the normal assembly of these organelles. In contrast the incorporation of acetate into cholesterol and cerebroside of Quaking myelin was decreased much more than microsomal synthesis. This latter result is consistent with a defect in the process of myclin membrane assembly
THYMIDINE PHOSPHORYLASE, THYMIDINE KINASE AND THYMIDYLATE SYNTHETASE ACTIVITIES IN CEREBRAL HEMISPHERES OF DEVELOPING CHICK EMBRYOS1
Authors: Hyndman A. G. , Zamenhof S. 
Published: October 2006

Abstract—The changes in activities of thymidine phosphorylase (EC 2.4.2.4), thymidine kinase (EC 2.7.1.75) and thymidylate synthetase (methylenetetrahydrofolate:dUrd‐5′‐P C‐methyltransferase, EC 2.1.1.‐) in the cerebral hemispheres of developing chick embryos were determined and compared with the course of DNA synthesis and of natural cell death in this organ.Thymidine phosphorylase activity reaches a broad maximum at the 12th to 14th day of incubation, followed by a rapid decrease. Thymidine kinase and thymidylate synthetase activities are highest at the earliest time studied (day 10) and decrease until day 14, followed by an increase from day 14 to 16 and a further decrease from day 16 through 1 day post‐hatching. The rate of DNA synthesis essentially follows these activities, but the increase at day 16 is not discernible.Our previous study revealed high DNA synthesis at day 10, with natural cell death concurring on days 12‐14, followed by another peak after day 16 (glial proliferation) and a decrease after day 16. It appears that thymidine phosphorylase activity reaches a maximum (days 12‐14) at the time of maximum cell death, which may be correlated with the degradative function of this enzyme. This was also the time for minimum activities of thymidine kinase and thymidylate synthetase; on the other hand, these activities reach a first (day 10) and second (day 16) maximum at the time of maximum DNA synthesis; this may be correlated with the synthetic functions of these enzymes.
RNA POLYMERASE ACTIVITY IN THE SUPERIOR CERVICAL GANGLION OF THE NEONATAL RAT: THE EFFECT OF NERVE GROWTH FACTOR
Authors: Huff Kenneth , Lakshmanan J. , Guroff Gordon 
Published: October 2006

Abstract—The activity of RNA polymerase in the superior cervical ganglia of the neonatal rat has been studied. The characteristics of the activity with respect to enzyme concentration, temperature, time, and ion concentrations are presented. Ionic conditions of the assay favoring polymerase I and polymerase II were each studied in the presence of specific inhibitors of DNA‐dependent RNA synthesis. The Km for GTP under either polymerase I or polymerase II conditions was found to be 10−5M, and the relative amounts of poly(A)‐containing RNA synthesized under both conditions was 4‐5%. A decrease in the activity of RNA polymerase with age has been observed.The time course of increased activity following treatment of the animals in vivo or treatment of the isolated ganglia in organ culture with nerve growth factor is presented. The increase in activity observed after the administration of nerve growth factor is discussed in terms of possible mechanisms of action of nerve growth factor in this tissue.
EFFECT OF THE ADMINISTRATION OF L‐5‐HYDROXYTRYPTOPHAN AND A MONOAMINE OXIDASE INHIBITOR ON GLUCOSE METABOLISM IN RAT BRAIN
Authors: Wong Kar‐Lit , Tyce Gertrude M. 
Published: October 2006

Abstract—The effects of the presence of large amounts of 5‐HT and of its precursor 5‐HTP in brain on cerebral utilization of glucose were studied. [U‐14C]Glucose was injected to fed rats that had previously been treated with L‐5‐HTP, L‐5‐HTP and an inhibitor—N‐[β‐(2‐chlorophenoxy)‐ethyl]‐cyclopropylamine hydrochloride (Lilly‐51641)‐of MAO, or Lilly‐51641 alone. Such treatment increased the concentrations of 5‐HTP and 5‐HT in the brain. After treatment with 5‐HTP and Lilly‐51641, and to a lesser extent with Lilly‐51641 alone, the concentration of glucose in plasma was increased. However, the uptake of glucose by the brain did not appear to be proportionately increased, and this suggested an impairment in this mechanism. After the administration of Lilly‐51641 alone and more especially of Lilly‐51641 plus 5‐HTP, the concentration of glucose in the brain was increased. This increase was thought to be due to an impairment of glucose utilization, because the flux of 14C from glucose to amino acids in the brain was reduced. The concentrations of most major amino acids in the brain were not greatly affected by these treatments. GABA and alanine concentrations in the brain were modestly increased after treatment with 5‐HTP alone or in combination with Lilly‐51641. The present results suggest that the metabolism of glucose to amino acids in the brain is altered when the concentration of 5‐HTP, or more especially that of 5‐HT, in the brain is increased.