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1.
Endogenous and xenobiotic sulphur-containing convulsant and non-convulsant compounds containing structural moieties of, or bearing a structural resemblance to, GABA and homocysteine were tested in binding studies for their potency in displacing the GABA-mimetic [3H]muscimol from specific, high-affinity sites (K
d=3.6 nM;B
max=3.94 pmol/mg protein) on freeze-thawed, Triton-treated calf-brain synaptic membranes. The xenobiotic convulsants, 4-mercaptobutyric acid (MBA), 3-mercaptopropionic acid (3-MPA) and 2-mercaptopropionic acid (2-MPA) were found to be two-site competitive inhibitors exhibiting apparent inhibition affinity constants (K
i
app
) of 5000 M, 3750 M, and 4800 M, respectively; while homocysteic acid (K
i
app
=4800 M) was shown to be a one-site partial competitive inhibitor. Intermediary metabolites of methionine: S-adenosyl-l-homocysteine,l-cysteine, the convulsantl-homocysteine, and its non-convulsant disulphide oxidation product, homocystine, were found to be one-site partial competitive inhibitors exhibitingK
i
app
values of 5750 M, 8350 M, 5000 M, and 510 M, respectively. The endogenous anticonvulsant neuroeffector, taurine, and the tripeptide, reduced glutathione (GSH) were shown to be, respectively, one-site (K
i=20 M) and two-site (K
i
app
=4300 M) competitive inhibitors of [3H]muscimol binding. These findings are discussed with regard to a previously proposed mechanism for the convulsant action of homocysteine. 相似文献
2.
Lawrence Spero 《Neurochemical research》1985,10(6):755-765
We have shown that diazepam (ED50 2.4 M), flunitrazepam (ED50 10.2 M) and Ro5-4864 (ED50 5 M) are able to enhance both total and specific [3H]phenytoin binding. Picrotoxin (IC50 1.43 M) and chloride, either NaCl or KCl (IC50 42.4 M) inhibit both the increase in total and specific binding of [3H]phenytoin, Ro 15-1788 does not. The optimum time for this enhancement was 3–4 hours. While the ED50's for the benzodiazepines are high their order of potency suggests that an involvement of both the peripheral type benzodiazepine receptor and the GABA-chloride ionophore complex is likely. Clonazepam (IC50 23 M), oxazepam (IC50 12 M) chlordiazepoxide (IC50 35 M) and Ro8682-10, a convulsant benzodiazepine (IC50 16 M) all inhibit both total and specific [3H]phenytoin binding. These effects were not blocked by chloride ions, picrotoxin or Ro 15-1788, and reached equilibrium within 45 minutes. This order of potency also parallels that for the peripheral benzodiazepine receptor in rat brain. These data suggest the presence of a micromolar benzodiazepine receptor site which may play a role in the control of CNS excitability. Nitrazepam, medazepam, bromazepam and the tetralobenzodiazepines U38335, U42794, U43434, and U37834 had no effect on total or specific [3H]phenytoin binding nor on the actions of the other benzodiazepines described in concentrations up to 50 M. 相似文献
3.
The effect of 8-isoprostanes on potassium (K+)-depolarization-evoked release of [3H]D-aspartate from bovine isolated retinae was investigated. Isolated bovine retinae were prepared for studies of K+-evoked release of [3H]D-aspartate using the Superfusion Method. Low concentrations of 8-isoPGF2(1–100 nM) inhibited whereas higher concentrations of this 8-isoprostane (100 nM–30 M) enhanced K+-induced [3H]D-aspartate overflow. The excitatory effect of 8-isoPGF2 was mimicked by thromboxane receptor agonist, U-46619 and blocked by thromboxane receptor antagonist, SQ 29,548 (10 M). Pretreatment of tissues with the cyclooxygenase (COX) inhibitor, flurbiprofen unmasked an inhibitory effect of high concentrations of 8-isoPGF2(1–30 M) on [3H]D-aspartate release that was attenuated by AH 6809 (10 M). In conclusion, 8-isoPGF2 exhibits a dual regulatory effect on K+-induced [3H]D-aspartate release in isolated bovine retinae. The inhibitory action caused by 8-isoPGF 2 is due to the activation of EP1/EP2 receptors while the excitatory effects are due to the activation of thromboxane receptors. 相似文献
4.
P. Ballerini R. Ciccarelli P. Di Iorio P. Giuliani F. Caciagli 《Neurochemical research》1995,20(6):697-704
[3H]Purine release from rat striatum astrocyte cultures was studied at 14 days in vitro (DIV). Superfusion of cultures with a Ca2+-free medium +0.5 mM ethylene glycol-bis(-aminoethylether)N,N,N,N-tetracetic acid (EGTA) reduced the electrically evoked [3H]purine release. Nimodipine only at the concentration of 10 M modified [3H]purine outflow whereas 0.1 M -conotoxin and 0.03–0.1 M nitrendipine reduced the evoked one. Superfusion of cultures with 0.1 M -conotoxin +0.1 M nitrendipine antagonized the evoked [3H]purine release similarly to each drug given alone. Neither nitrendipine nor -conotoxin influenced the uptake of45Ca2+ by the cultures. The treatment of cells with the Ca2+ agonist Bay K 8644 did not affect [3H]purine release or the45Ca2+ uptake. The drug did not either alter [Ca2+]i, evaluated by loading the cells with 3 M Fura-2/AM. 10–30 M 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester (TMB-8), a blocker of intracellular Ca2+ discharge, significantly reduced the evoked [3H]purine release. On the other hand, 2 M thapsigargin, an inhibitor of the ion store Ca2+ ATPase, was able to increase either the culture [3H]purine release or the [Ca2+]i. Together, the findings indicate that voltage-sensitive calcium channels (VSCCs) of the neuronal N and L-types are not involved in the modulation of [3H]purine release from rat cultured astrocytes whereas Ca2+ coming from intracytoplasmic stores seems to play a prevailing role. Moreover, agents which block VSCCs seem to be able to affect [3H]purine outflow with mechanisms other than VSCC gating. 相似文献
5.
We have investigated whether muscarinic receptors modulate the release of [3H]ACh elicited by secretagogues that act by different mechanisms in rat cerebral cortical synaptosomes. Oxotremorine (10 M) reduced the calcium-dependent [3H]ACh release induced by mild K+-depolarization (10 and 15 mM K+), but not that by higher K+ concentrations. The ACh-release induced by A23187 (0.2–5 g/ml), liposomes laden with 113 mM CaCl2, or 4-aminopyridine (1–10 mM) was not modulated by oxotremorine. Ouabain (100 M)-induced release of [3H]ACh was reduced by oxotremorine in normal but not calcium-free KR, indicating that extracellular calcium-uptake but not Na+, K+-ATPase activity may be necessary for release-modulation. With respect to possible second messenger systems, dibutyrylcyclic AMP (0.1–2 mM), dibutyrylcyclic GMP (0.1–2 mM), forskolin (100 M), and phorbol ester (0.3–3 g/ml) were without effect on release or release-modulation. These results are consistent with an involvement of K+-channels and voltage-sensitive calcium-channels in the muscarinic release-inhibition process. They argue against an involvement of Na+, K+-ATPase, adenylate cyclase, guanylate cyclase, and phosphatidylinositol turnover in the release-modulation process. 相似文献
6.
Two constitutive acetoacetyl-CoA (AcAc-CoA) reductases were purified from Methylobacterium rhodesianum MB 126, an NADPH-linked d(-)--hydroxybutyryl-CoA forming reductase (enzyme A) and an NADH-and NADPH-linked l(+)--hydroxybutyryl-CoA forming reductase (enzyme B). Enzyme A and B give apparent K
m values of 15 M and 30 M for AcAc-CoA, 18 M for NADPH and 30 M for NADH, respectively. They are inhibited by AcAc-CoA at concentrations higher than 25 M and 50 M, respectively. The contribution of the two reductases to poly--hydroxybutyrate synthesis is discussed. 相似文献
7.
Klavs Holtug Al Shipley Vibeke Dantzer Ove Sten-Knudsen Erik Skadhauge 《The Journal of membrane biology》1991,122(3):215-229
Summary Hen coprodeum absorbs sodium electrogenically and, when stimulated by theophylline, secretes chloride. In this study the vibrating microprobe technique was used to localize the transport of these ions to intestinal villi/folds and crypts. With the isolated, stretched epithelium, controlled by light microscopy and scanning electron microscopy, in open circuit, currents were inward, 40±7 A/cm2, 50 m vertically above villi, and outward, 36±7 A/cm2 above crypts. The currents decayed exponentially to near zero at 300 m with the same length constant. A physical model simulating the observed loci of current sources and sinks predicts potential profiles consistent with our data. Extrapolation of the currents gives a surface potential of 45 V, negative on villi and positive above crypts. Short circuiting increased villus current to 86±27 A/cm2 at 50 m, and amiloride treatment reduced it to –8 A/cm2; in both cases crypt currents were abolished. The inward currents are compatible with sodium absorption. Induction of chloride secretion after amiloride treatment, resulted in current circuits similar to those induced by sodium absorption, with villus currents of 23±7 A/cm2. This is in accord with chloride secretion at the villi. Quantitative estimates of crypt number (860/cm2) and opening diameter (15 m), in conjunction with isotopic measurements of active and electrical potential-driven ion fluxes demonstrate, however, that only 4% of the potential-driven co-ion transport occurs through the crypts. This indicates that nearly all chloride secretion comes from the sodium-absorbing villar area. Were the chloride secretion to occur solely from the crypts, the current should have been in the opposite direction and 10,000-fold larger. 相似文献
8.
The effect of L-cysteine sulfinic acid (CSA) and L-homocysteic acid (HCA) on the release of tritiated -amino butyric acid ([3H]GABA), from the external plexiform layer (EPL) of the rat olfactory bulb, was compared with that of glutamate. These amino acids induced release of GABA was strongly inhibited by the glutamate uptake blocker, pyrrolidine-2,4-dicarboxylate (2,4,PDC) (50 M), while it was not inhibited by the specific GABA uptake blockers nipecotic acid (0.5 mM) or NO-711 (5M). Only the HCA induced GABA release was 60% inhibited by -alanine (0.5 mM), a glial GABA uptake blocker and 78% by the NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (AP-5) (100 M). The non-NMDA receptor antagonists 6-cyano-2,3-dihydroxy-7-nitro-quinoxaline (CNQX) up to 500 M had no effect on HCA or CSA stimulated GABA release. These results bring evidence for an excitatory role of HCA and CSA together with glutamate on GABAergic neuronal or glial elements, in the olfactory bulb. This role could be mediated through the reversal of the glutamate or/and the glial GABA transporter and through the activation of a NMDA type receptor. 相似文献
9.
DOPA synthesis from phenylalanine was studied in PC12 cells incubated with m-hydroxybenzylhydrazine, to inhibit aromatic L-amino acid decarboxylase. DOPA synthesis rose with increasing concentrations of either phenylalanine or tyrosine; maximal rates (~55 pmol/min/mg protein for tyrosine; ~40 pmol/min/mg protein for phenylalanine) occurred at a medium concentration of ~10 M for either amino acid. The Km for either amino acid was about 1 M (medium concentration). At tyrosine concentrations above 30 M, DOPA synthesis declined; inhibition was observed at higher concentrations for phenylalanine (300 M). These effects were most notable in the presence of 56 mM potassium. Measurements of intracellular phenylalanine and tyrosine suggested the Km for either amino acid is 20–30 M; maximal synthesis occurred at 120–140 M. In the presence of both phenylalanine and tyrosine, DOPA synthesis was inhibited by phenylalanine only at a high medium concentration (1000 M), regardless of medium tyrosine concentration. The inhibition of DOPA synthesis by high medium tyrosine concentrations was antagonized by high medium phenylalanine concentrations (100, 1000 M). Together, the findings indicate that for PC12 cells, phenylalanine can be a significant substrate for tyrosine hydroxylase, is a relatively weak inhibitor of the enzyme, and at high concentrations can antagonize substrate inhibition by tyrosine. 相似文献
10.
Synaptosomal membranes accumulate 3–6 times more Ca2+ in the presence of ATP (50–1000 M) than basal Ca2+ accumulation (-ATP). The location of this Ca2+ accumulation appears to reside on the cytosolic face of the synaptosome since lysed synaptosomes accumulate 4-times more Ca2+ than intact synaptosomes. The inclusion of mitochondrial inhibitors, oligomycin (0.7 g/ml), sodium azide (100 M) and dinitrophenol (100 M) differentiate mitochondrial from nonmitochondrial Ca2+ accumulation under conditions that are [Ca2+]- and ATP-dependent. In the presence of low concentrations of ATP (<150 M) and Ca
free
2+
(2.5 or 6.8 M), Ca2+ accumulation occurs as one process in both lysed synaptosomal membranes and purified synaptic plasma membranes in the presence and/or absence of MI. When ATP levels are increased (>200 M), the Ca2+ accumulation process remains independent of the presence of mitochondrial inhibitors when Ca
free
2+
=2.5 M. When Ca
free
2+
is increased to 6.8 M, mitochondrial inhibitors differentiate mitochondrial from nonmitochondrial accumulation. These studies suggest that optimal conditions for the measurement of Ca2+ accumulating mechanisms in synaptosomal membranes depend on both [Ca2+] and ATP. Use of these assay conditions provide evidence that ATP-dependent Ca2+ uptake may be a viable mechanism for the regulation of synaptosomal Ca2+ levels. 相似文献
11.
Moussa Cel-H Mitrovic AD Vandenberg RJ Provis T Rae C Bubb WA Balcar VJ 《Neurochemical research》2002,27(1-2):27-35
(2S,1'S,2'R)-2-(Carboxycyclopropyl)glycine (L-CCG III) was a substrate of Na+-dependent glutamate transporters (GluT) in Xenopus laevis oocytes (IC50 13 and 2 M for, respectively, EAAT 1 and EAAT 2) and caused an apparent inhibition of [3H]L-glutamate uptake in mini-slices of guinea pig cerebral cortex (IC50 12 M). In slices (350 M) of guinea pig cerebral cortex, 5 M L-CCG III increased both the flux of label through pyruvate carboxylase and the fractional enrichment of glutamate, GABA, glutamine and lactate, but had no effect on total metabolite pool sizes. At 50 M L-CCG III decreased incorporation of 13C from [3-13C]-pyruvate into glutamate C4, glutamine C4, lactate C3 and alanine C3. The total metabolite pool sizes were also decreased with no change in the fractional enrichment. Furthermore, L-CCG III was accumulated in the tissue, probably via GluT. At lower concentration, L-CCG III would compete with L-glutamate for GluT and the changes probably reflect a compensation for the missing L-glutamate. At 50 M, intracellular L-CCG III could reach > 10 mM and metabolism might be affected directly. 相似文献
12.
The presence of active mitochondria and oxidative metabolism is shown to be essential to maintain low inhibition levels by ethanol of the growth rate (), fermentation rate (v) or respiration rate () of Saccharomyces cerevisiae wild type strain S288C. Cells which have respiratory metabolism show K
i (ethanol inhibition constant) values for , v and , higher (K
i>1 M) than those of petite mutants or grande strains grown in anaerobiosis (K
i=0.7 M). In addition, the relationship between or v and ethanol concentration is linear in cells with respiratory metabolism and exponential in cells lacking respiration. When functional mitochondria are transferred to petite mutants, the resulting strain shows K
i values similar to those of the grande strain and the inhibition of and v by increasing ethanol concentrations becomes linear. 相似文献
13.
Callus was initiated from immature leaf and stem segments of rose (Rosa hybrida cv. Landora) and subcultured every four weeks on a basal medium of half-strength Murashige & Skoog (1962) salts plus 30 g l-1 sucrose (1/2 MS) and supplemented with 2.2 M BA, 5.4 M NAA and 2.2–9.0 M 2,4-D. Embryogenic callus and subsequently somatic embryos were obtained from 8-week-old callus culture on 1/2 MS+2.2 M BA+0.05 M NAA+0.3 M GA3+200–800 mg l-1 L-proline. Long-term cultures were established and maintained for up to 16 months by repeated subculture of embryogenic callus on L-proline deficient medium. About 12% of cotyledonary stage embryos taken from cultures cold-stored at 8±1°C for 4 days germinated on 1/2 MS+2.2 M BA+0.3 M GA3+24.7 M adenine sulphate.Abbreviations BA
benzyladenine
- NAA
-naphthaleneacetic acid
- 2,4-D
2,4-dichlorophenoxyacetic acid
- GA3
gibberellic acid 相似文献
14.
Falqueto EB Massensini AR Moraes-Santos T Gomez MV Romano-Silva MA 《Cellular and molecular neurobiology》2002,22(5-6):819-826
1. Voltage-gated Na+ channels are responsible for initiation and conduction of action potentials. The arrival of an action potential at nerve terminal increases intracellular Na+ and Ca2+ concentrations. Calcium entry into neurons through voltage-dependent calcium channels is associated with a variety of intracellular processes. Scorpion neurotoxins have been used as tools to investigate mechanisms involved in neurotransmitter release. Tityustoxin (TsTX) is an -type toxin that delays Na+-channel inactivation. Toxin- (TiTX-) is a -type toxin that induces Na+-channel activation at resting potentials.2. In the present work, we describe the effects of both toxins on [3H]acetylcholine ([3H]ACh) release from rat cerebrocortical synaptosomes, in the presence or absence of the calcium channels blockers: -conotoxin-GVIA (-CgTx), 1 M; -agatoxin-IVA (-Aga), 30 nM; -conotoxin-MVIIC (-MVIIC), 1 M; or verapamil, 1M.3. TsTX evokes [3H]ACh release in a concentration-dependent manner with a gradual increase up to saturation at concentrations of 500 nM. However, release of ACh evoked by TiTX- was not linear regarding the toxin concentration. The [3H]-ACh release evoked by TsTX or TiTX- was partially inhibited by -CgTx or -Aga, and blocked with -MVIIC. Verapamil (1 M) had no effect. Tetrodotoxin blocked [3H]ACh release evoked by both toxins.4. These results show that different actions on Na+-channels produce different effects on [3H]ACh release with involvement of distinct presynaptic Ca2+-channels, which supports the idea that sodium channels may modulate neurotransmitter release. 相似文献
15.
Plant regeneration has been achieved from long-term cell suspension cultures established from leaf derived callus of tepary bean (Phaseolus acutifolius). The proportion of densely cytoplasmic cells in suspension culture increased when cultured in the L-6 medium with 54 M NAA and 2 M KN. Filtration of the cells at each of five consecutive subcultures resulted in the isolation of a plant regenerating cell line (TB 686), which is being maintained in L-6 medium with 4.5 M 2,4-D and 2.3 M zeatin. Differentiated green cell aggregates were obtained when cells from maintenance medium were transferred to the same medium with 10 M BA. Embryo-like structures developed from these aggregates on L-6 medium with 2.3 M zeatin, 0.69 M GA3 and 1.5 M NAA. Plantlets regenerated from these structures when they were cultured on L-6 medium with 7.0 M NAA and 1.0 M KN. Plant regeneration from the cell line remained relatively constant for 270 days. Regenerated plants were grown to maturity in the greenhouse.Abbreviations BA
Benzyladenine
- 2,4-D
2,4-dichlorophenoxyacetic acid
- GA3
Gibberellic acid
- IPA
Isopentenyladenine
- KN
Kinetin
- NAA
Naphthaleneacetic acid
- AA
Amino acid medium (Toriyama and Hinita, 1985)
The research was sponsored by United States Agency for International Development, Washington D.C., Cooperative Agreement DAN-4137-A-00-4053-00 相似文献
16.
Nitric oxide modulation of dopamine D2 and D3 receptor binding was examined using [125I]epidepride (D2) and (+)7-hydroxy-N,N-di-n-[3H]propyl-2-aminotetralin([3H](+)-7-OH-DPAT, D3). Nitric oxide, generated by i.c.v. injection of S-nitroso-N-acetyl-penicillamine (SNAP; 5 g or 10 g), significantly increased the density of [3H](+)-7-OH-DPAT binding sites (39% and 134%, respectively) in the striatum 24 hours post-injection in the absence of Gpp(NH)p, representing an upregulation of either D3, receptors or high affinity D2 receptors. In the presence of 10 M Gpp(NH)p, D3 receptor upregulation was maintained in both the 5 g (increased 35%) and 10 g SNAP (increased 44%) groups. [3H](+)-7-OH-DPAT binding was reduced in both striatum and nucleus accumbens in the presence of 10 M Gpp(NH)p compared to binding in the absence of Gpp(NH)p, suggesting an upregulation of D3 receptors. Administration of SNAP did not alter total specific [125I]epidepride binding in either brain region. These data suggest that; 1) D3 receptor density is modified following nitric oxide generation, and 2) the density of high affinity D2 receptors identified by [3H](+)-7-OH-DPAT increases in the striatum, but decreases in the nucleus accumbens. 相似文献
17.
The effects of prolonged oral administration (21 days) of fumonisin B1 (FB1) and aflatoxin B1 (AFB1) were evaluated on male Wistar rats. The animals were housed in individual metabolic cages and submitted to the following treatments: 1-0 g AFB1 + 0 mg FB1/100g bw.; 2-72 g AFB1+ 0 mg FB1/100 g bw; 3-0 g AFB1 + 0.5 mg FB1 g bw; 4-0 g AFB1 + 1.5 mg FB1/100 g bw; 5-72 g AFB1 + 0.5 mg FB1/100g bw; 6-72 gAFB1 + 1.5 mg FB1/100g bw. On day 21, the rats were sacrificed for evaluation. The results showed that treated animals presented differences in body weight and absolute/relative weights of liver and kidney as well as altered hepatic function and cholesterol blood levels. Rats fed with the greatest doses of AFB1 and FB1 gained less weight (2.79 g/day) at the end of the experimental period; their blood concentrations of liver enzymes aspartate aminotransferase (AST) and alkaline phosphatase (AP) were above control levels (130.35 /l and 471.00 /l, respectively). Blood cholesterol increased in the groups treated with the highest dose ofFB1 or FB1 associated with AFB1. Histopathology revealed the occurrence of apoptosis in the liver of rats exposed to FB1. The association of aflatoxin B1 with fumonisin B1 at higher dose probably potentiated the effects of the higher dose of fumonisin B1acting singly.This revised version was published online in October 2005 with corrections to the Cover Date. 相似文献
18.
Histamine transport has been characterized in cultured astroglial cells of rat brain. The kinetics of [3H]-histamine uptake yielded a Km of 0.19±0.03 M and a Vmax of 3.12±0.75 pmol×mg protein–1×min–1. Transport system revealed high affinity for histamine and an approximately ten times higher capacity than that shown in cultured glial cells of chick embryonic brain. Ouabain which interferes with utilization of ATP to generate ion gradients, and the replacement of Na+ with choline inhibited the initial rate of uptake showing a strong Na+-dependency and suggesting the presence of a tightly coupled sodium/histamine symporter. Dissipation of K+-gradient (in>out) by high K+ or by K+-channel blockers, BaCl2, (100 M), quinine (100 M) or Sparteine (20 M) produced also remarkable inhibitions in the uptake of [3H]-histamine. Impromidine, a structural histamine-analogue could inhibit the uptake non-competitively in a range of concentrations of 1 to 10 M with a Ki value of 2.8 M, indicating the specificity of the uptake. [3H]histamine uptake measurements carried out by using a suspension of dissociated hypothalamic cells, of rat brain showed a strong gliotoxin-sensitivity and yielded a Km of 0.33±0.08 M; and a Vmax of 2.65±0.35 pmoles×mg protein–1×min–1. The uptake could be reversed by incubating the cells in histamine-free Krebs medium. The [3H]histamine efflux was sensitive to Na+ omission, ouabain treatment and high K+ or K+ channel blockers, resulting in marked elevations in the efflux. Data indicate that glial uptake of histamine is a high affinity, Na+-dependent and electrogenic, driven by an inward-oriented sodium ion gradient and an outward-oriented potassium ion gradient and functions as part of histamine inactivation, at least in a shunt mechanism.Abbreviations used HA
histamine
- [3H]HA
[2.5-3H]-histamine
-
dl--aAA
dl-alpha-aminoadipic acid
- (Na++K+) ATP-ase
sodium and potassium activated adenosine triphosphatase
- SAH
S-Adenosyl-d-Homocysteine
- HNMT
histamine-N-methyltransferase 相似文献
19.
The activities and kinetics of the enzymes G6PDH (glucose-6-phosphate dehydrogenase) and 6PGDH (6-phosphogluconate dehydrogenase) from the mesophilic cyanobacterium Synechococcus 6307 and the thermophilic cyanobacterium Synechococcus 6716 are studied in relation to temperature. In Synechococcus 6307 the apparent K
m's are for G6PDH: 80M (substrate) and 20M (NADP+); for 6PGDH: 90M (substrate) and 25M (NADP+). In Synechococcus 6716 the apparent K
m's are for G6PDH: 550M (substrate) and 30M (NADP+); for 6PGDH: 40M (substrate) and 10M (NADP+). None of the K
m's is influenced by the growth temperature and only the K
m's of G6PDH for G6P are influenced by the assay temperature in both organisms. The idea that, in general, thermophilic enzymes possess a lower affinity for their substrates and co-enzymes than mesophilic enzymes is challenged.Although ATP, ribulose-1,5-bisphosphate, NADPH and pH can all influence the activities of G6PDH and 6PGDH to a certain extent (without any difference between the mesophilic and the thermophilic strain), they cannot be responsible for the total deactivation of the enzyme activities observed in the light, thus blocking the pentose phosphate pathway.Abbreviations G6PDH
glucose-6-phosphate, dehydrogenase
- 6PGDH
6-phosphogluconate dehydrogenase
- G6P
glucose-6-phosphate
- 6PG
6-phosphogluconate
- RUDP
ribulose-1,5-bisphosphate
- Tricine
N-Tris (hydroxymethyl)-methylglycine 相似文献
20.
Clozapine and several other antipsychotic/antidepressant drugs that fully or partially block GABAA receptors were tested at concentrations that reversed the inhibitory effect of 1 M GABA on 35S-t-butylbicyclophosphorothionate ([35S]TBPS) binding to rat forebrain membranes only about 20–30%, here designated core fractions. Clozapine at 10 M reverses 1 M GABA 25 ± 4.0% (n = 23) (its core fraction). Fourty three compounds were tested alone, and pairwise together with 10 M Clozapine. The core fractions of some of the compounds yielded significant additive reversals together with 10 M Clozapine, while others did not. A group of 14 compounds of which 7 are clinically effective antipsychotic drugs, including Chlorprothixene, Clomacran, Clopipazan, Fluotracen, Sulforidazine, Thioproperazine, and cis-Thiothixene, were statistically non-additive with 10 M Clozapine, suggesting that all of these drugs selectively block the same core population of GABAA receptors as Clozapine. These non-additivities also suggest that Clozapine at 10 M fully saturates a subset of GABAA receptors blocked by 1 M GABA. Therefore, Clozapine probably blocks 2 or more types of GABAA receptors, but only half of the receptors that are sensitive to 1 M GABA. A second group of 12 compounds of which 6 are clinically active antidepressant/antipsychotic drugs including Amoxapine, Clothiapine, Dibenzepine, Inkasan (Metralindole), Metiapine and Zimelidine were slightly, but significantly, additive with Clozapine suggesting that these compounds block most of Clozapine's core fraction, plus a small additional fraction. A third group consisted of ten compounds that yielded larger (R > 80) and statistically highly significant additivities with Clozapine. Complete additivity was obtained with Bathophenanthroline disulfonate, and Isocarboxazid, suggesting that they block GABAA receptors other than those blocked by 10 M Clozapine. Seven classical GABAA receptor blockers, also tested at concentrations yielding 21 to 33% reversal alone, were all significantly additive with 10 M Clozapine, but in no case was the additivity complete. The largest additivity was obtained with Pitrazepine (21%) and the smallest with Tubocurarine (9%). These results provide further support for the notion that selective blockade of the same subset of GABAA receptors may contribute to the clinical antipsychotic/antidepressant effects of Clozapine. The Bopt values for Clozapine are 50 ± 1.7% and 26 ± 2.6% ( n = 3) in whole rat forebrain and cerebellum, respectively, confirming that clozapine-sensitive GABAA receptors are unevenly distributed in the brain. The sedative and anxiolytic properties of Clozapine and other antipsychotic drugs may be due to selective blockade of GABergic disinhibition at certain interneurons. 相似文献