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101.
The rapid increase in protein synthesis that occurs on addition of insulin (1 mU/ml) to stepped-down 3T3 cells was blocked by pre-incubation of the cells with pertussis toxin. Cholera toxin on the other hand stimulated protein synthesis and this effect was insensitive to actinomycin D and inhibited by pro-treatment of the cells with phorbol dibutyrate to deplete cell protein kinase C. Insulin was found to cause a rapid and transient increase in diacylglycerol (DAG) synthesis. The insulin-induced increase in diacylglycerol was blocked by pertussis toxin. Exogenous DAG (10 M) stimulated protein synthesis within 1 hour. The results suggest that insuIin stimulates ribosomal activity through a signal mechanism that involves a G-protein mediated activation of phospholipase C to increase DAG levels. 相似文献
102.
Jorma Palvimo Anitta Mahonen Pekka H. Menp 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1987,931(3)
Chromosomal high-mobility-group (HMG) proteins have been examined as substrates for calcium/phospholipid-dependent protein kinase C. Protein kinase C from rat brain phosphorylated efficiently both HMG 14 and HMG 17 derived from calf thymus and the reactions were calcium/phospholipid-dependent. About 1 mol of 32P was incorporated per mol of HMG 14 and HMG 17. Phosphopeptide mapping suggested that the same major site was phosphorylated in both proteins at serine. The apparent Km values for HMG 14 and HMG 17 were about 5 μM. HMG 14, HMG 17 and the five histone H1 subtypes prepared from rat thymus, liver and spleen were phosphorylated by the kinase. HMG 14 and HMG 17 from transformed human lymphoblasts (Wi-L2) were also phosphorylated in a calcium/phospholipid-dependent manner. HMG 1 and HMG 2 from the tissues examined were found to be poor substrates for the kinase. 相似文献
103.
The photoacoustic (PA) characteristics (energy storage and heat dissipation) of photosystem II (PSII) core-enriched particles from barley were studied (i) in conditions where there was electron flow, i.e., in the presence of a combination of the electron acceptor K3 Fe (CN)6, referred to as FeCN, and the electron donor diphenylcarbazide (DPC), and (ii) in conditions where electron flow was suppressed, i.e., in the absence of FeCN and DPC. The experimental data show that a decrease of heat dissipation with a minimum at 540 nm can be interpreted as energy storage resulting from the presence of pheophytin (Pheo) in the PSII particles. On account of the capability of the PA method to measure the energy absorbed by the chromophores which is converted to heat, it is suggested that the PA detection of Pheo present in the PSII complex will permit to clarify the function of processes involving non-radiative relaxation of excited states in P680-Pheo-QA interactions.Abbreviations -Car
-Carotene
- Chl
Chlorophyll
- DPC
Diphenylcarbazide
- EPR
Electron Paramagnetic Resonance
- FeCN
potassium ferricyanide
- HEPES
N-2-hydroxyethylenepiperazine-N-2-ethanesulfonate
- P680
reaction center of PSII
- PA
Photoacoustic
- Pheo
pheophytin
- PSI
photosystem I
- PSII
photosystem II
- QA
primary electron acceptor of PSII 相似文献
104.
A. De Marco A. M. Petros R. A. Laursen M. Llinás 《European biophysics journal : EBJ》1987,14(6):359-368
The interaction of the isolated human plasminogen kringle 4 with the four -amino acid ligands -aminocaproic acid (ACA), N-acetyl-l-lysine (AcLys), trans-aminomethyl(cyclohexane)carboxylic acid (AMCHA) and p-benzylaminesulfonic acid (BASA) has been further characterized by 1H-NMR spectroscopy at 300 and 600 MHz. Pronounced high-field shifts, reaching 3 ppm, are observed for AMCHA resonances upon binding to kringle 4, which underscores the relevance of ligand lipophilic interactions with aromatic side chains at the binding site. Ligand titration curves for the nine His and Trp singlets found in the kringle 4 aromatic spectrum reveal a striking uniformity in the kringle response to the various ligands. The average binding curves exhibit a clear Langmuir absorption isotherm saturation profile and the data were analyzed under the assumption of one (high affinity) binding site per kringle. Equilibrium association constants (K
a
) and first order dissociation rate constants (k
off) were derived from linearized expressions of the Langmuir isotherm and of the spectral line-shapes, respectively. The results for the four ligands, at 295 K, pH* 7.2, indicate that: (a) AMCHA exhibits the strongest binding (K
a
=159 mM
-1) and ACA the weakest (K
a
=21 mM
–1) with AcLys and BASA falling in between; (b) ACA dissociates readily (k
off = 5.3 × 103 s–1) and AMCHA associates the fastest (k
off = 2.0 × 108
M
–1 s–1) while the kinetics for BASA exchange is relatively slow (k
off = 0.8 × 103 s–1, k
on = 0.6 × 108
M
–1s–1); (c) the ligand-binding kinetics is close to diffussion-controlled.Abbreviations ACA
-aminocaproic acid
- AcLys
N-acetyl-l-lysine
- AMCHA
t-aminomethyl(cyclohexane)carboxylic acid
- BASA
p-benzylaminesulfonic acid
- K4
kringle 4
- NOE
nuclear Overhauser effect
- ppm
parts-per-million
- pH*
glass electrode pH reading uncorrected for deuterium isotope effects
-
K
a
ligand-kringle 4 equilibrium association constant
-
k
off
ligand-kringle 4 dissociation rate constant
-
k
on
ligand-kringle 4 association rate constant 相似文献
105.
Intravenous (IV) infusions of neurotensin (NT) in anesthetized guinea pigs elicited dose-dependent pressor effects and tachycardia. Both effects were significantly reduced or abolished in guinea pigs given a chronic treatment with the neurotoxin capsaicin. In guinea pig isolated atria NT evoked a positive inotropic and chronotropic effect. Both effects were completely abolished in atria derived from capsaicin-treated guinea pigs. The positive inotropic and chronotropic effects of NT in guinea pig atria were mimicked by capsaicin and calcitonin gene-related peptide (CGRP). These results were interpreted as an indication that NT produces its cardiovascular effects in guinea pigs by activating capsaicin-sensitive sensory neurons. 相似文献
106.
Carroll D. Arnett Joanna S. Fowler Robert R. MacGregor David J. Schlyer Alfred P. Wolf Bengt Långström Christer Halldin 《Journal of neurochemistry》1987,49(2):522-527
The distribution of carbon-11-labeled L-deprenyl, an irreversible inhibitor of monoamine oxidase type B (MAO-B), was determined in the baboon brain by positron emission tomography. The irreversible blood-to-brain transfer constant (influx constant, Ki) was measured using a complete metabolite-corrected arterial plasma concentration curve. This influx constant was used as a measure of functional enzyme activity for sequential determinations of MAO-B recovery following a single high dose of unlabeled l -deprenyl. The half-life for turnover of MAO-B was thus determined to be 30 days. Using appropriate irreversible inhibitors, this procedure should be generally useful for determining enzyme turnover rates in any organ in vivo and can be applied to some human studies as well. 相似文献
107.
M. B. Emerit S. El Mestikawy H. Gozlan J. M. Cossery R. Besselievre A. Marquet M. Hamon 《Journal of neurochemistry》1987,49(2):373-380
The synthesis of a tritiated derivative of the 5-HT1A photoaffinity probe 8-methoxy-2-[N-n-propyl, N-3-(2-nitro-4-azidophenyl)aminopropyl]aminotetralin ([3H]8-methoxy-3'-NAP-amino-PAT) allowed the use of this probe for attempting the irreversible labeling of specific binding sites in rat brain membranes. Sodium dodecyl-sulfate-polyacrylamide gel electrophoresis of proteins solubilized from hippocampal microsomal membranes that had been incubated with 20 nM [3H]8-methoxy-3'-NAP-amino-PAT under UV light revealed a marked incorporation of 3H label into a 63-kilodalton protein termed PI. As expected of a possible correspondence between PI and 5-HT1A receptor binding sites, 3H labeling by the photoaffinity probe could be prevented by selective 5-HT1A ligands such as 8-hydroxy-2-(di-n-propylamino)tetralin, ipsapirone, buspirone, and gepirone and by N-ethylmaleimide, but not by the 5-HT2 antagonist ketanserin, noradrenaline- and dopamine-related drugs, monoamine oxidase inhibitors, and chlorimipramine. Furthermore, the regional and subcellular distributions of PI were identical to those of specific 5-HT1A binding sites. These results indicated that the binding subunit of the 5-HT1A receptor is a 63-kilodalton protein with a functionally important sulfhydryl group(s). 相似文献
108.
Rat sciatic nerve cytosol contains a phosphodiesterase of the phospholipase C type that catalyzes the hydrolysis of inositol phospholipids, with preferences of phosphatidylinositol 4'-phosphate (PIP) greater than phosphatidylinositol (PI) much greater than phosphatidylinositol 4',5'-bisphosphate (PIP2), at a pH optimum of 5.5-6.0 and at maximum rates of 55, 13, and 0.7 nmol/min/mg protein, respectively. Analysis of reaction products by TLC and formate exchange chromatography shows that inositol 1,2-cyclic phosphate (83%) and diacylglycerol are the major products of PI hydrolysis. [32P]-PIP hydrolysis yields inositol bisphosphate, inositol phosphate, and inorganic phosphate, indicating the presence of phosphodiesterase, phosphomonoesterase, and/or inositol phosphate phosphatase activities in nerve cytosol. Phosphodiesterase activity is Ca2+-dependent and completely inhibited by EGTA, but phosphomonoesterase activity is independent of divalent cations or chelating agents. Phosphatidylcholine (PC) and lysophosphatidylcholine (lysoPC) inhibit PI hydrolysis. They stimulate PIP and PIP2 hydrolysis up to equimolar concentrations, but are inhibitory at higher concentrations. Both diacylglycerols and free fatty acids stimulate PI hydrolysis and counteract its inhibition by PC and lysoPC. PIP2 is a poor substrate for the cytosolic phospholipase C and strongly inhibits hydrolysis of PI. However, it enhances PIP hydrolysis up to an equimolar concentration. 相似文献
109.
The highest concentration of neurokinin A-like immunoreactivity and substance P-like immunoreactivity in the guinea pig small intestine was associated with the myenteric plexus-containing longitudinal muscle layer. Chromatographic analysis of extracts of this tissue demonstrated the presence of neurokinin A and neuropeptide K but the probable absence of neurokinin B. A fraction of synaptic vesicles of density 1.133 +/- 0.003 g/ml was prepared from the myenteric plexus-containing tissue by density gradient centrifugation in a zonal rotor and was enriched 29 +/- 12-fold in the concentration of neurokinin A-like immunoreactivity and 43 +/- 13-fold in the concentration of substance P-like immunoreactivity. This fraction was separated from the fraction of vasoactive intestinal peptide-containing vesicles (density, 1.154 +/- 0.009 g/ml). Chromatographic analysis of lysates of the vesicles indicated the presence of neurokinin A but not neuropeptide K. It is postulated that beta-pre-protachykinin is processed to substance P, neurokinin A, and neuropeptide K in the cell bodies of myenteric plexus neurons but that conversion of neuropeptide K to neurokinin A takes place during packaging into storage vesicles for axonal transport. The data are consistent with the proposal that neurokinin A and substance P are stored in the same synaptic vesicle, but the possibility of cosedimentation of different vesicles of very similar density cannot be excluded. 相似文献
110.
Differential Postnatal Development of Monoamine Oxidases A and B in the Blood-Brain Barrier of the Rat 总被引:2,自引:2,他引:0
Abstract: We studied the monoamine metabolizing mitochondrial enzyme, monoamine oxidase (MAO), in cerebral microvessels obtained from postnatally developing rats by measuring the specific binding of [3 H]pargyline, an irreversible inhibitor of MAO, and the rate of oxidation of three known MAO substrates: benzylamine, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and tryptamine. MAO activity increased postnatally, with the greatest increase occurring in the second week and reaching a peak at 3 weeks of age. A concomitant increase in MAO of the cerebral cortex also occurred, but was several-fold less than that of cerebral microvessels. Using clorgyline and deprenyl, relatively specific inhibitors of MAO-A and MAO-B, we showed that cerebral microvessels contain both forms of MAO at all ages, but there was a major preponderance in the postnatal development of MAO-B. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analyses of rat microvessels after [3 H]pargyline binding also showed two distinct bands of radioactivity at all ages. These two bands corresponded to molecular weights of ∼6.5,000 for MAO-A and -60,000 for MAO-B. SDS-PAGE resuits of brain microvessels obtained from 1-, 14-, and 42-day-old rats confirm the differential postnatal development of MAO-B in rat brain microvessels. 相似文献