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41.
The mechanism of hypercholesterolemia effect of Cu2+ deficiency was studied in rats. There was increased activity of hepatic hydroxymethylglutaryl-coenzyme A reductase and increased
incorporation of labelled acetate into free cholesterol of liver in the Cu2+ deficient rats. Incorporation of label into ester cholesterol was however decreased in the liver. Concentration of bile acids
in the liver was not significantly altered. Increase in the incorporation of labelled acetate into serum cholesterol and increase
in the concentration of cholesterol and apo B in the low density lipoproteins + very low density lipoproteins fractions were
observed. Activity of lipoprotein lipase of the extrahepatic tissues decreased in the Cu2+ deficient rats. 相似文献
42.
The galactose-binding lectin of human Placenta has been Purified to homogeneity by affinity chromatograPhy on asialo-fetuin
column. The Protein, extractable from the tissue only with lactose is aPParently membrane-bound. Molecular weight determination
of native Protein and subunit indicated a dimer of l3.4 kDa subunits. Inhibition of haemagglutination with various saccharides
indicate that thiodigalactoside is the best inhibitor followed by lactose. However,P-nitroPhenyl-and 1-O-methyl derivatives of galactose showed that α-anomers inhibited slightly better than β-anomer. Modification
of amino acid residues indicated involvement of arginine, lysine and histidine residues at the saccharidebinding site. Cysteine
residue modificatioin also abolished haemagglutinating activity. Amino acid comPosition of the lectin is also Presented. 相似文献
43.
Amplification of chirality based upon the association of nucleic acid strands of opposite handedness
C. A. A. van Boeckel G. M. Visser R. A. Hegstrom J. H. van Boom 《Journal of molecular evolution》1987,25(2):100-105
Summary It is proposed that nucleotide strands of opposite handedness may strongly associate and thereby provide the key step of a mechanism for the amplification of a small enantiomeric excess in an initially near-racemic mixture of poly- or oligonucleotides. This hypothesis, if confirmed by experimentation, may have important implications for the question of the origin of biomolecular chirality. The results of preliminary NMR experiments are given, which do show evidence of a strong association between pentanucleotide RNA strands whose monomers have opposite chirality. Simple kinetic equations are solved to demonstrate the conditions under which such association can produce amplification of chirality. 相似文献
44.
Donal A. Hickey Bernhard F. Benkel Poppo H. Boer Yves Genest Sumaia Abukashawa Gerard Ben-David 《Journal of molecular evolution》1987,26(3):252-256
Summary We constructed a cDNA library for the beetle,Tribolium castaneum. This library was screened using a cloned amylase gene fromDrosophila melanogaster as a molecular probe. Beetle amylase cDNA clones were isolated from this bank, and the nucleotide sequence was obtained for a cDNA clone with a coding capacity for 228 amino acids. Both the nucleotide sequence and predicted amino acid sequence were compared to our recent results forD. melanogaster alpha-amylases, along with published sequences for other alpha-amylases. The results show that animal alpha-amylases are highly conserved over their entire length. A borader comparison, which includes plant and microbial alpha-amylase sequences, indicates that parts of the gene are conserved between prokaryotes, plants, and animals. We discuss the potential importance of this and other enzyme-coding genes for the construction of molecular phylogenies and for the study of the general question of molecular clocks in evolution. 相似文献
45.
Arthur L. Weber 《Journal of molecular evolution》1987,25(1):7-11
Summary Reaction ofDl-serine and adenosine-5-phosphorimidazolide in the presence of adenosine-5-(O-methylphosphate) and imidazole resulted in the stereoselective synthesis of the aminoacyl nucleotide ester 2(3)-O-seryl-adenosine-5-(O-methylphosphate). The enantiomeric excess ofd-serine incorporated into 2(3)-O-seryl-adenosine-5-(O-methylphosphate) was about 9%. Adenylyl-(5N)-serine and an unknown product also incorporated an excess ofd-serine; however, serylserine showed an excess ofl-serine. The relationship of these results to the origin of the biological pairing ofl-amino acids and nucleotides containingd-ribose is discussed. 相似文献
46.
Kirsi-Marja Marnela Vince Varga Gábor Dibó Pekka Lähdesmäki 《Journal of neurochemistry》1987,48(4):1090-1092
To elucidate the position of the peptide bond in glutamyl-taurine this dipeptide was extracted from calf brain synaptic vesicles and subjected to paper electrophoresis. It was analyzed further in an automatic amino acid analyzer prior and subsequent to acid hydrolysis. Both alpha- and gamma-forms were found to be present in approximately equal amounts. 相似文献
47.
Calcium-Dependent and-Independent Release of Glutamate from Synaptosomes Monitored by Continuous Fluorometry 总被引:18,自引:9,他引:9
David G. Nicholls Talvinder S. Sihra Jose Sanchez-Prieto 《Journal of neurochemistry》1987,49(1):50-57
An enzyme-linked fluorometric assay is described for the continuous monitoring of the unidirectional efflux of glutamate from guinea-pig synaptosomes. Glutamate efflux from freshly suspended, polarized synaptosomes occurs at 0.35-0.39 nmol min-1 mg of protein-1 and is not significantly affected by external Ca2+. KCl depolarization (30 mMKCl) in the absence of Ca2+ doubles this rate, whereas in the presence of Ca2+, the initial kinetics of the assay are consistent with the release in the first 5 s of 0.6 nmol mg of protein-1. The final extent of Ca2+-dependent release amounts to 1.9 nmol mg of protein-1, or 8.5% of the total intrasynaptosomal glutamate content. Preincubation of synaptosomes at 30 degrees C for 2 h before depolarization leads to a decrease in Ca2+-independent release and an increase in Ca2+-dependent release, consistent with an intrasynaptosomal relocation of the amino acid. 相似文献
48.
Pretreatment of rats with the excitatory amino acid antagonist 2-amino-7-phosphonoheptanoic acid (2-APH; 0.5 mmol/kg, i.p.) protected against insulin-induced clonic seizures. Complete protection was observed in 38% of the rats and partial protection in an additional 50%. Lesioning of the corticostriatal pathway by frontal cortical ablation caused decreases in the striatal levels of aspartate (-28%) and glutamate (-18%), an increase in striatal glutamine level (45%), and decreased high-affinity uptake of D-[3H]aspartate (-27%) in the lesioned dorsal neostriatum. Insulin-induced hypoglycemia caused a predicted sharp increase in aspartate level (165%) and decreased glutamate (-20%) and glutamine (-38%) levels in the intact striatum. Pretreatment of rats with 2-APH significantly reversed the insulin-induced changes in striatal aspartate, glutamate, and glutamine levels, especially in the intact hemisphere. In normoglycemic control rats, the "metabolic," i.e., concentration in the lesioned hemisphere, aspartate pool constituted 72% and the "synaptic," i.e., the concentration difference between the intact and lesioned hemispheres, 28% of the total striatal aspartate pool. 2-APH had no effect on the level of "metabolic" aspartate in the striata of normoglycemic rats but caused an almost complete suppression of "synaptic" aspartate. Following insulin-induced hypoglycemia, the "metabolic" aspartate pool doubled, whereas the "synaptic" aspartate pool increased 3.5-fold in the absence of 2-APH. The insulin-induced rise in "synaptic" aspartate level was almost completely blocked by 2-APH (a 5% rise instead of a 3.5-fold rise).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
49.
The reaction of racemization in which the L amino acids are reversibly converted into the corresponding D amino acids, proceeds in geological environment at such a slow rate that it may be used as a geochronometer. However, in fossils several parameters may affect the rate of racemization, i.e. moisture, surface, pH buffer and metal cations. This work consists of a systematic study of total amino acid content in fossil bones from two neanderthalian sites. The amino acid distributions of all specimens were determined and compared to that of fresh bone. The D/L amino acid were quantified and expressed in terms of age as a function of the temperature. The results led us to consider the «La Roquette» site older than «Les Canalettes» site. 相似文献
50.
Summary The lipid and sterol content and composition of three lipid fractions (free fatty acids/ sterols, triacylglycerols and sterol/triterpenoid esters) extracted from three stem discs of Pinus sylvestris were assessed to investigate metabolic changes related to heartwood formation. The wood was separated into (1) cambial zone, (2) outer sapwood, (3) inner sapwood, (4) transition zone, (5) outer heartwood and 6) inner heart-wood. The fractions were separated by thin-layer chromatography (TLC) and analysed by gas-liquid chromatography (GLC). The amount of fatty acids of sapwood triacylglycerols was about 1.5% (dry wt.) but a large reduction occurred in the transition zone. In contrast, noticeable amounts of free fatty acids were present only in the heart-wood. The most important fatty acids in the sapwood fractions were 16:0, 18:0, 18:1, 18:2 (the dominant fatty acid in all fractions), 18:3 and 20:3. Together 18:1 and 18:2 formed about 70% of the total triacylglycerol fatty acids. Of the sterol/ triterpenoid esters, 18:2 and 18:3 were predominant. The fatty acid composition of all fractions changed in the transition zone. The sterols found were sitosterol, stigmastanol, campesterol and campestanol. The amount of sterol esters increased towards the heartwood, and the amount of free sterols was lowest in the inner sapwood. Sitosterol was the dominant sterol in both free sterols and sterol esters. 相似文献