共查询到20条相似文献,搜索用时 997 毫秒
1.
J K Ladha P Rowell W D Stewart 《Biochemical and biophysical research communications》1978,83(2):688-696
5-hydroxylysine, an analogue of glutamate and lysine, causes production by N2-fixing A. cylindrica; it also reversibly inhibits GS activity in vitro but has no effect on alanine dehydrogenase or GOGAT. On adding 5-hydroxylysine intracellular pools of glutamine, glutamate and aspartate decrease; those of alanine and serine increase. 5-hydroxylysine alleviates the inhibitory effect of on heterocyst production and C2H2 reduction and in cultures results in heterocyst synthesis and in C2H2 reduction. The data suggest that the GS-GOGAT pathway is the sole route of importance in primary assimilation in A. cylindrica, that alone does not inhibit nitrogenase and heterocyst production, and that GS and/or a product is involved in regulating the production of both. 相似文献
2.
Kathryn L. Desphande Jon R. Katze James F. Kane 《Biochemical and biophysical research communications》1980,95(1):55-60
Glutamate synthase, an important enzyme in the assimilation of ammonia, was measured in cultures of grown with different nitrogen sources. An attempt was made to correlate the specific activity to the intracellular levels of five metabolites of glutamate metabolism: aspartate, glutamate, glutamine, alanine and . An inverse relationship was found between the activity of glutamate synthase and the pool level of glutamine. We propose that the intracellular concentration of glutamine is an important element in controlling the level of glutamate synthase. 相似文献
3.
W R Scowcroft A H Gibson J D Pagan 《Biochemical and biophysical research communications》1976,73(2):516-523
Nitrogenase activity in agar cultures of cowpea rhizobia, strain 32H1, was rapidly inhibited by but this was relieved by increased O2 tension. Inhibition was more rapid than that caused by inhibitors of protein synthesis and was not relieved by methionine sulfoximine or methionine sulfone. Under conditions were nitrogenase activity was inhibited by , glutamine synthetase and glutamate synthase were substantially unaffected. Glutamate dehydrogenase was undetected in either nitrogenase active or inhibited cultures. These results indicate that inhibition of nitrogenase activity in strain 32H1 is not effected through glutamine synthetase regulation of nitrogenase synthesis. 相似文献
4.
(1) +/electron acceptor ratios have been determined with the oxidant pulse method for cells of denitrifying Paracoccus denitrificans oxidizing endogenous substrates during reduction of O2, NO?2 or N2O. Under optimal H+-translocation conditions, the ratios , , for reduction to N2 and for reduction to N2O were 6.0–6.3, 4.02, 5.79 and 3.37, respectively. (2) With ascorbate/N,N,N′,N′-tetramethyl-p-phenylenediamine as exogenous substrate, addition of NO?2 or N2O to an anaerobic cell suspension resulted in rapid alkalinization of the outer bulk medium. , for reduction to N2 and for reduction to N2O were ?0.84, ?2.33 and ?1.90, respectively. (3) The ratios, mentioned in item 2, were not altered in the presence of and the triphenylmethylphosphonium cation. (4) A simplified scheme of electron transport to O2, NO?2 and N2O is presented which shows a periplasmic orientation of the nitrite reductase as well as the nitrous oxide reductase. Electrons destined for NO?2, N2O or O2 pass two H+-translocating sites. The acceptor ratios predicted by this scheme are in good agreement with the experimental values. 相似文献
5.
(1) A quantitative study has been made of the binding of ouabain to the ( in homogenates prepared from brain tissue of the hawk moth, Manduca sexta. The results have been compared to those obtained in bovine brain microsomes. (2) The insect brain ( will bind ouabain either in the presence of Mg2+ and Pi, (‘Mg2+, Pi’ conditions) or in the presence of Na+, Mg2+, and an adenine nucleotide (‘nucleotide’ conditions) as is the case for the bovine brain (. The binding conditions did not alter the total number of receptor sites measured at high ouabain concentrations in either tissue. (3) Potassium ion decreases the affinity (increases the ) of ouabain to the M. sexta brain ( under both binding conditions. However, ouabain binding is more sensitive to K+ inhibition under the nucleotide conditions. In bovine brain ouabain binding is equally sensitive to K+ inhibition under the both conditions. (4) The enzyme-ouabain complex has a rate of dissociation that is 10-fold faster in the M. sexta preparation than in the bovine brain preparation. Because of this, the M. sexta ( has a higher for ouabain binding and is less sensitive to inhibition by ouabain than the bovine brain enzyme. (5) This data supports the hypothesis that two different conformational states of the M. sexta ( can bind ouabain. 相似文献
6.
Dennis W. Jung Guey-Yueh Shi Gerald P. Brierley 《Archives of biochemistry and biophysics》1981,209(2):356-361
Depletion of mitochondrial divalent cations by addition of the ionophore A23187 results in a marked increase in passive exchange activity. The exchange is activated by increasing pH and temperature and inhibited by added divalent cations. The reaction is independent of the amount of A23187 present, but depends on the concentration of external K+ (Km = 25 mm). Intramitochondrial 42K+ in cation-depleted mitochondria exchanges passively with external Na+ and Li+, but not with choline+. The evidence suggests that removal of mitochondrial divalent cations by A23187 activates the endogenous exchange component of the mitochondrion and that the activated exchanger promotes cation/cation exchange in the absence of a metabolic pH gradient. 相似文献
7.
Showdomycin inhibited pig brain ( with pseudo first-order kinetics. The rate of inhibition by showdomycin was examined in the presence of 16 combinations of four ligands, i.e., Na+, K+, Mg2+ and ATP, and was found to depend on the ligands added. Combinations of ligands were divided into five groups in terms of the magnitude of the rate constant; in the order of decreasing rate constants these were: (1), (2) , , and none, (3) , and , (4) and , , , and ATP. The highest rate was obtained in the presence of Na+, Mg2+ and ATP. The apparent concentrations of Na+, Mg2+ and ATP for half-maximum stimulation of inhibition () were 3 mM, 0.13 mM and 4μM, respectively. The rate was unchanged upon further increase in Na+ concentration from 140 to 1000 mM. The rates of inhibition could be explained on the basis of the enzyme forms present, including E1, E2, ES, E1-P and E2-P, i.e., E2 has higher reactivity with showdomycin than E1, while E2-P has almost the same reactivity as E1-P. We conclude that the reaction of ( proceeds via at least four kinds of enzyme form (E1, E2, E1 · nucleotide and EP), which all have different conformations. 相似文献
8.
9.
Sam W. Woo Anthony W. Linnane Phillip Nagley 《Biochemical and biophysical research communications》1982,109(2):455-462
strain DC5-E2 that lacks mtDNA () can be cotransformed with a mixture of mtDNA and the plasmid YEp13 (LEU2/2μ/pBR322) to produce Leu+ transormants which, on being mated to tester strains, generate respiratory competent diploids (such events are denoted marker rescue). In this work strain DC5-E2 was transformed with recombinant molecules consisting of a mtDNA segment including the gene inserted into YEp13. The Leu+ transformants made with the recombinant plasmids were unable to rescue testers carrying mutations in the region, in contrast to Leu+ cotransformants made with mixtures of YEp13 and mtDNA. We conclude that marker rescue events occur as a result of interactions between the mtDNA of the tester and the mtDNA sequences introduced by transformation. Such interactions cannot occur when the latter mtDNA is forced to replicate in covalent association with YEp13, probably in the nucleus. 相似文献
10.
Diploid embryos which are homozygous for the t12 mutation die at the morula stage. In the current studies, ova from heterozygous () females were fertilized in vitro with spermatozoa from males. The fertilized ova were immediately placed into media containing cytochalasin B to prevent second polar body formation, producing +/+/+, +/+/t12, +/t12/t12, and t12/t12/t12 embryos. The subsequent development of these triploid embryos was compared with that of diploid +/+, , and embryos developing from ova which were also fertilized in vitro with spermatozoa from males but which were not treated with cytochalasin B immediately following gamete coincubation. The data show that those triploid embryos which possess a wild-type allele and two mutant alleles are phenotypically wild type while those possessing three mutant alleles are not phenotypically distinguishable from their diploid () counterparts. Like embryos, t12/t12/t12 embryos die at the morula stage, prior to blastocoelic cavity formation. 相似文献
11.
A potent inhibitor of activity was purified from Sigma equine muscle ATP by cation- and anion-exchange chromatography. The isolated inhibitor was identified by atomic absorption spectroscopy and proton resonance spectroscopy to be an inorganic vanadate. The isolated vanadate and a solution of V2O5 inhibit sarcolemma with an of 1 μM in the presence of 1 mM acid (EGTA), 145 mM NaCl, 6mM MgCl2, 15 mM KCl and 2 mM synthetic ATP. The potency of the isolated vanadate in increased by free Mg2+. The inhibition is half maximally reversed by 250 μM epinephrine. Equine muscle ATP was also found to contain a second inhibitor which depends on the sulfhydryl-reducing agent dithioerythritol for inhibition. This unknown inhibitor does not depend on free Mg2+ and is half maximally reversed by 2 μM epinephrine. Prolonged storage or freeze-thawing of enzyme preparations decreases the susceptibility of the to this inhibitor. The adrenergic blocking agents, propranolol and phentolamine, do not block the catecholamine reactivation. The inhibitors in equine muscle ATP also inhibit highly purified from shark rectal gland and eel electroplax. The inhibitors in equine muscle ATP have no effect on the other sarcolemmal ATPases, Mg2+-ATPase, Ca2+-ATPase and . 相似文献
12.
Inhibitors of glutamine synthetase cause derepression of nitrogenase biosynthesis in the presence of in the photosynthetic bacterium Rhodopseudomonas capsulata. A new derepressor of nitrogenase biosynthesis, β-N-oxalyl-L-α,β-diaminopropionic acid (ODAP), is here compared with the widely used L-methionine-DL-sulfoximine (MSX). With both compounds, a quantitative correlation has been observed between inhibition of glutamine synthetase and derepression of nitrogenase biosynthesis. We also find that both MSX and ODAP inhibit nitrogenase activity in vivo in R. capsulata. The latter effect seems to be indirect and related to the previously reported reversible inhibition of nitrogenase activity in vivo by . As a control it was observed that neither nor MSX nor ODAP inhibit nitrogenase activity in vivo in Clostridium pasteurianum. 相似文献
13.
Stanley B. Brown Haris Hatzikonstantinou David G. Herries 《Biochimica et Biophysica Acta (BBA)/General Subjects》1978,539(3):338-351
The dimerization of deuteroferrihaem in aqueous solution has been investigated using a parameter, named the dimerization index (Robs). This is defined as the ratio of extinction coefficients at wavelengths corresponding to Soret band maxima for the monomeric and dimeric species, respectively. For solutions containing mainly monomeric species, Robs > 2, whereas for solutions containing mainly dimeric species Robs < 1.A computer programme has been applied to determine values of the dimerization constant, K, defined as: .Phosphate buffer anions and Tris · HCl buffer enhanced dimerization. Monovalent and divalent cations also increased dimerization, but in a specific manner. The magnitudes of their effects increased in the order . Values of K were determined for several concentrations of Na+ and Sr2+. These data are interpreted in terms of a stabilization of the ferrihaem dimer by the formation of ion triplets with the added cation ‘sandwiched’ between carboxyl residues of the adjacent ferrihaem monomeric units. General guidelines are recommended for the choice of conditions which minimize dimerization. 相似文献
14.
Soluble consisting predominantly of αβ-units with below 170 000 was prepared by incubating pure membrane-bound (35–48 μmol Pi/min per mg protein) from the outer renal medulla with the non-ionic detergent dodecyloctaethyleneglycol monoether (C12E8). and potassium phosphatase remained fully active in the detergent solution at C12E8/protein ratios of 2.5–3, at which 50–70% of the membrane protein was solubilized. The soluble protomeric was reconstituted to Na+, K+ pumps in phospholipid vesicles by the freeze-thaw sonication procedure. Protein solubilization was complete at C12E8/protein ratios of 5–6, at the expense of partial inactivation, but and potassium phosphatase could be reactivated after binding of C12E8 to Bio-Beads SM2. At C12E8/protein ratios higher than 6 the activities were irreversibly lost. Inactivation could be explained by delipidation. It was not due to subunit dissociation since only small changes in sedimentation velocities were seen when the C12E8/protein ratio was increased from 2.9 to 46. As determined immediately after solubilization, was 7.4 S for the fully active , 7.3 S for the partially active particle, and 6.5 S for the inactive particle at high C12E8/protein ratios. The maximum molecular masses determined by analytical ultracentrifugation were 141 000–170 000 dalton for these protein particles. Secondary aggregation occurred during column chromatography, with formation of enzymatically active or with S and apparent molecular masses in the range 273 000–386 000 daltons. This may reflect non-specific time-dependent aggregation of the detergent micelles. 相似文献
15.
Purified b-type cytochrome oxidase from Rhodopseudomonas capsulata was incorporated into phospholipid vesicles to measure proton extrusion with pulses of ferrocytochrome c for one oxidase turnover. In accordance with the pH shift of its midpoint potential, the purified oxidase showed a proton extrusion of 0.24 with uptake of 1 from the liposomes for the reduction of oxygen to water. This proton translocation could only be observed in the presence of valinomycin +K+ and was not inhibited by DCCD. Oxidase preparations from the first purification step, which contain other protein compounds especially a membrane-bound cytochrome c but not the ubiquinol-cytochrome c2-oxidoreductase showed a pumping activity of 0.9 , which was inhibited by DCCD for nearly 75%. Inhibition of the electron transfer was not observed, which could be explained by a ‘molecular slipping’ of proton extrusion and electron transfer. Proton extrusion from two oxidase-turnovers was only 80% of that from one turnover. The proton pumping of the b-type oxidase strongly depended on the enzyme/phospholipid ratio. 相似文献
16.
Furosemide () inhibits a proportion of the total passive (ouabain-insensitive) K+ influx into primary chick heart cell cultures (85%), BC3H1 cells (75%), MDCK cells (40%) and HeLa cells (57%). This action of furosemide upon K+ influx is independent of ( inhibition since the furosemide-sensitive component of the K+ influx is identical in the presence and absence of ouabain (). For HeLa cells the passive, furosemide-sensitive component of K+ influx is markedly dependent upon the external K+, Na+ and Cl? content. Acetate, iodide and nitrate are ineffective as substitutes for Cl?, whereas Br? is partially effective. Partial Cl? replacement by NO3? gave an apparent affinity of 100 mM [Cl]. Na+ replacement by choline+ abolishes the furosemide-sensitive component, whereas Li+ replacement reduces this component by 48%. Partial Na+ replacement by choline+ gives an apparent affinity of 25 mM [Na+]. Variation in the external K+ content gives an affinity for the furosemide-sensitive component of approx. 1.0 mM. Furosemide inhibition of the passive K+ inflúx is of high affinity, half-maximal inhibition being observed at furosemide. Piretanide () and phloretin () inhibit the same component of passive K+ influx as furosemide; ethacrynic acid and amiloride () partially so. The stilbene, SITS (), was ineffective as an inhibitor of the furosemide-sensitive component. 相似文献
17.
ADP and Pi-loaded membrane vesicles from l-malate-grown Bacillus alcalophilus synthesized ATP upon energization with . ATP synthesis occurred over a range of external pH from 6.0 to 11.0, under conditions in which the total protonmotive force was as low as ?30 mV. The phosphate potentials (ΔGp) were calculated to be 11 and 12 kcal/mol at pH 10.5 and 9.0, respectively, whereas the values in vesicles at these two pH values were quite different (?40 ± 20 mV at pH 10.5 and ?125 ± 20 mV at pH 9.0). ATP synthesis was inhibited by KCN, gramicidin, and by N,N′-dicyclohexylcarbodiimide. Inward translocation of protons, concomitant with ATP synthesis, was demonstrated using direct pH monitoring and fluorescence methods. No dependence upon the presence of Na+ or K+ was found. Thus, ATP synthesis in B. alcalophilus appears to involve a proton-translocating ATPase which functions at low . 相似文献
18.
Using guanidinium and n-butylammonium cations (C+) as models for the positively charged side chains in arginine and lysine, we have determined the association constants with various oxyanions by potentiometric titration. For a dibasic acid, H2A, three association complexes may exist: ; ; . For guanidinium ion and phosphate, K1M = 1.4, K1D = 2.6, and K2D = 5.1. The data for carboxylates indicate that the basicity of the oxyanion does not affect the association constant: acetate, pKa = 4.8, K1M = 0.37; formate, pKa = 3.8, K1M = 0.32; and chloroacetate, pKa = 2.9, K1M = 0.43, all with guanidinium ion. Association constants are also reported for carbonate, dimethylphosphinate, benzylphosphonate, and adenylate anions. 相似文献
19.
Quercetin inhibited a dog kidney ( preparation without affecting for ATP or for cation activators, attributable to the slowly-reversible nature of its inhibition. Dimethyl sulfoxide, a selector of E2 enzyme conformations, blocked this inhibition, while the K+-phosphatase activity was at least as sensitive to quercetin as the ( activity, all consistent with quercetin favoring E1 conformations of the enzyme. Oligomycin, a rapidly-reversible inhibitor, decreased the for ATP and the for cation activators, and its inhibition was also diminished by dimethyl sulfoxide. Although oligomycin did not inhibit the K+-phosphatase activity under standard assay conditions, a reaction presumably catalyzed by E2 conformations, its effects are nevertheless accommodated by a quantitative model for that reaction depicting oligomycin as favoring E1 conformations. The model also accounts quantitatively for effects of both dimethyl sulfoxide and oligomycin on , for substrate, and for K+, as well as for stimulation of phosphatase activity by both these reagents at low K+ but high Na+ concentrations. 相似文献
20.
The action of ATP and its analogs as well as the effects of alkali ions were studied in their action on the ouabain receptor. One single ouabain receptor with a dissociation constant () of 13 nM was found in the presence of () and (). pH changes below pH 7.4 did not affect the ouabain receptor. Ouabain binding required Mg2+, where a curved line in the Scatchard plot appeared. The affinity of the receptor for ouabain was decreased by K+ and its congeners, by Na+ in the presence of (), and by ATP analogs (ADP-C-P, ATP-OCH3). Ca2+ antagonized the action of K+ on ouabain binding. It was concluded that the ouabain receptor exists in a low affinity (Rα) and a high affinity conformational state (Rβ). The equilibrium between both states is influenced by ligands of . With 3 mM Mg2+ a mixture between both conformational states is assumed to exist (curved line in the Scatchard plot). 相似文献