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961.
Effect of Monovalent Cations on Na+ /Ca2+ Exchange and ATP-Dependent Ca2+ Transport in Synaptic Plasma Membranes 总被引:1,自引:0,他引:1
Two Ca2+ transport systems were investigated in plasma membrane vesicles isolated from sheep brain cortex synaptosomes by hypotonic lysis and partial purification. Synaptic plasma membrane vesicles loaded with Na+ (Na+i) accumulate Ca2+ in exchange for Na+, provided that a Na+ gradient (in leads to out) is present. Agents that dissipate the Na+ gradient (monensin) prevent the Na+/Ca2+ exchange completely. Ca2+ accumulated by Na+/Ca2+ exchange can be released by A 23187, indicating that Ca2+ is accumulated intravesicularly. In the absence of any Na+ gradient (K+i-loaded vesicles), the membrane vesicles also accumulate Ca2+ owing to ATP hydrolysis. Monovalent cations stimulate Na+/Ca2+ exchange as well as the ATP-dependent Ca2+ uptake activity. Taking the value for Na+/Ca2+ exchange in the presence of choline chloride (external cation) as reference, other monovalent cations in the external media have the following effects: K+ or NH4+ stimulates Na+/Ca2+ exchange; Li+ or Cs+ inhibits Na+/Ca2+ exchange. The ATP-dependent Ca2+ transport system is stimulated by increasing K+ concentrations in the external medium (Km for K+ is 15 mM). Replacing K+ by Na+ in the external medium inhibits the ATP-dependent Ca2+ uptake, and this effect is due more to the reduction of K+ than to the elevation of Na+. The results suggest that synaptic membrane vesicles isolated from sheep brain cortex synaptosomes possess mechanisms for Na+/Ca2+ exchange and ATP-dependent Ca2+ uptake, whose activity may be regulated by monovalent cations, specifically K+, at physiological concentrations. 相似文献
962.
In frozen-thawed repeatedly washed rat cortical synaptic membranes, Ca2+ (1-5 mM) decreased the binding of [3H]muscimol whereas it increased the binding of [3H]gamma-aminobutyric acid (GABA). However, the binding of [3H]GABA was decreased by the same extent as the binding of [3H]muscimol when the membranes were incubated with baclofen (a selective ligand for the GABAB binding site) and Ca2+. Scatchard analysis of [3H]muscimol binding revealed that Ca2+ reduced the density of GABA binding sites without affecting the dissociation constant. Ca2+ was more potent than Ba2+, Mg2+ was ineffective, and the Ca2+ antagonist La3+ stimulated [3H]muscimol binding. The inhibition of [3H]muscimol binding by Ca2+ was not influenced by calmodulin (50 micrograms/ml), trifluoperazine (10(-5) M), verapamil (10(-6) M), quinacrine (10(-4) M), cordycepin (0.1 mM), leupeptin (20 microM), or soybean trypsin inhibitor (0.1 mg/ml). Moreover, the effect of Ca2+ was additive to that of GABA-modulin. These results indicate that Ca2+ decreases the number of GABAA binding sites while unveiling GABAB binding sites. 相似文献
963.
The accumulation of transported materials in cut axons is demonstrated by the light and electron microscopic immunocytochemical localization of substance P and enkephalin in the caudal medulla and cervical spinal cord of adult rat. Two days following unilateral knife-cuts in the caudal medulla or spinal (C2-C3) levels, substance P and enkephalin-like immunoreactivity (SPLI and ELI) are detected in lesioned axons located rostral and caudal to the transection. Rostrally, SPLI and ELI are detected in the lateral reticular region and ventrolateral fasciculus corresponding to the location of previously identified bulbospinal pathways. Caudally, previously unidentified, propriospinal pathways showing SPLI are detected in the dorsal columns and in the dorsolateral fasciculus. In contrast, ELI is found caudal to the transection only in the reticular region of the medulla. For both peptides, immunoreactivity is present throughout axons containing numerous large, dense core, and small clear vesicles. These results support the concept of both particulate and soluble modes of transport for substance P and enkephalin within axons of the central nervous system. 相似文献
964.
Z. Krupa 《Photosynthesis research》1983,4(3):229-239
Thylakoid membranes obtained from bean chloroplasts treated with bean galactolipase or phospholipase A2 (from Crotalus terr. terr.) showed marked changes in their polypeptide patterns when separated on SDS-PAGE. The obtained results have been discussed with regard to the relationship between chloroplast lipids and polypeptides originating from chlorophyll-protein complexes of bean thylakoids. A coexistence between galactolipids and the peripheral antennae in PS I complex and LHCP3 as well as a conspicuous role of phospholipids in PSI and PSII centre chlorophyll-protein complexes has to be underlined.Abbreviations CP1
chlorophyll a-protein complex of PSI
- CPa
chlorophyll a-protein complex of PSII
- D10
digitonin subchloroplast particles enriched in PSII
- D144
digitonin subchloroplast particles enriched in PSI
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- LHCP1–3
light harvesting chlorophyll a/b protein complexes
- PAGE
polyacrylamide gel electrophoresis
- PSI
photosystem I
- PSII
photosystem II
- SDS
sodium dodecyl sulphate
- TCA
trichloroacetic acid
- Tricine
N-Tris-(hydroxymethyl)-methylglycine
- Tris
Tris-(hydroxymethyl)-aminomethan 相似文献
965.
Perry Barrett Peter-M. Kloetzel John Sommerville 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1983,740(4)
During early oogenesis in amphibia, most of the 5 S RNA and tRNA is stored in a ribonucleoprotein particle that sediments at 42 S. In Xenopus laevis the 42 S particle contains two major proteins: of Mr 48 000 (P48) and 43 000 (P43). It is shown that heterogeneity in composition of the 42 S particle reflects a changing situation whereby initially, both 5 S RNA and tRNA are complexed with P48 (1 molecule 5 S RNA: 1 molecule P48; 2 or 3 molecules tRNA: 1 molecule P48), but later, tRNA becomes increasingly associated with P43 (in a 1:1 ratio) although 5 S RNA remains complexed with a cleavage product of P48. These changes relate to the eventual utilization of the excess 5 S RNA and tRNA in ribosome assembly and protein synthesis. 相似文献
966.
Howard M. Laten Jane Harris Cramer Robert H. Rownd 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1983,741(1):1-6
By culturing Saccharomyces cerevisiae in growth medium containing Mg35SO4, we have determined the extent and variation of tRNA thiolation in this yeast. We find that 5-methoxycarbonylmethyl-2-thiouridine (mcm5s2U)1 is the major, if not only, thiolated derivative in S. cerevisiae tRNA. In addition, a comparison of the chromatographic mobility of mcm5s2Up on cellulose thin layers with those reported for unknown uridine derivatives found in purified yeast tRNA digests, leads to the conclusion that at least two of these tRNAs contain this modification. 相似文献
967.
Cristoph Zimmer Gerhard Luck Eckhard Birch-Hirschfeld Roland Weiss Federico Arcamone Wilhelm Guschlbauer 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1983,741(1):15-22
Different binding affinities of various distamycin analogs including the deformylated derivative with poly(dA-dC)·poly(dG-dT) were investigated using CD measurements. The inhibitory effect of distamycins on the DNAase I cleavage activity of DNA duplexes strongly supports the binding data. The base specificity of the ligand interaction with duplex DNA depends on the chain length of distamycin analogs. Netropsin, distamycin-2 and the deformylated distamycin-3 show no binding to dG·dC containing sequences at moderate ionic strength and are classified as highly dA·dT specific. In contrast distamycin having three, four or five methylpyrrolecarboxamide groups also forms more or less stable complexes with dG·dC-containing duplexes. These ligands possess a lower basepair specificity. The correlation between binding behavior and oligopeptide structure shows that presence of the number of hydrogen acceptor and donor sites determines the basepair and sequence specificity. The additional interaction with dG·dC pairs becomes essential when the number of hydrogen acceptor sites exceeds n = 3. 相似文献
968.
Carol S. Surowy Nathan A. Berger 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1983,740(1):8-18
Acceptor proteins for poly(adenosine diphosphoribosyl)ation were determined in resting human lymphocytes, in lymphocytes with N-methyl-N′-nitro-N-nitrosoguanidine-induced DNA damage and in lymphocytes stimulated to proliferate by phytohemagglutinin. Kinetic studies showed that the increase in ADP-ribosylation which occurred in response to N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) treatment was greater in magnitude but more transient in duration than that which occurred in phytohemagglutinin-stimulated cells. Gel electrophoretic analyses revealed that MNNG treatment and phytohemagglutinin stimulation both caused an increase in ADP-ribosylation of poly(ADP-ribose) polymerase and core histones. In MNNG-treated cells, an increase in ADP-ribosylation of histone H1 was also observed. In contrast, phytohemagglutinin-stimulated cells showed no increase in ADP-ribosylation of histone H1. In MNNG-treated cells there was also ADP-ribosylation of a protein of molecular weight 62 000, while in phytohemagglutinin-stimulated cells there was a marked increase in ADP-ribosylation of a protein of molecular weight 96000. MNNG treatment of phytohemagglutinin-stimulated cells produced a pattern of ADP-ribosylation that appeared to be due to the combined effects of the individual treatments. 3-Aminobenzamide effectively inhibited ADP-ribosylation under all treatment conditions. 相似文献
969.
Michael Ready Sandra Bird Gail Rothe J.D. Robertus 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1983,740(1):19-28
It has been known for some time that pokeweed antiviral protein acts by enzymatically inhibiting protein synthesis on eucaryotic ribosome systems. The site of this action is known to be the ribosome itself. In this paper we show that the pokeweed antiviral protein reaction against ribosomes is a strong function of salt concentrations, where 160 mM K+ and 3 mM Mg2+ retards the reaction, while 20 mM K+ and 2 mM Mg2+ allows maximum reaction rate. It is also shown, however, that an unidentified protein in the postribosomal supernatant solution, together with ATP, allows the ribosome to be attacked even in the presence of high salt. Kinetic analysis of the antiviral protein reaction has been carried out under both sets of conditions, and reveals that the turnover number for the enzyme is about 300–400 mol/mol per min. in each case. The Km for ribosomes is 1 μM in the presence of low salt and 0.2 μM at higher salt in the presence of postribosomal supernatant factors plus ATP. The antiviral protein reaction is also shown to be pH dependent and is controlled by a residue with pKa value of approx. 7.0, apparently a histidine. Stoichiometric reaction of the enzyme with iodoacetamide results in a significant loss of antiribosomal activity. 相似文献
970.
Venkataraman Amarnath Traci L. Miller Arthur D. Broom 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1983,741(2):224-229
Poly(5-fluoro-2′-deoxyuridylic acid) was synthesized and its properties were compared with those of poly(dT) and poly(dU). It readily complexed with poly(dA). The 1:1 complex melted at about 20°C lower than poly(dA) · poly(dT). A triple-stranded helix, poly(dA)·2 poly(dF5U) was formed only in high salt (2.0 M NaCl). 相似文献