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1.
Guanylate cyclase from crude homogenates of vegetative has been characterized. It has a pH optimum of 8.0, temperature optimum of 25°C and requires 1 mM dithiothreitol for optimal activity. It strongly prefers Mn++ to Mg++ as divalent cation, requires Mn++ in excess of GTP for detectable activity, and is inhibited by high Mn++ concentrations. It has an apparent Km for GTP of approximately 517 μM at 1 mM excess Mn++.The specific activity of guanylate cyclase in vegetative homogenates is 50–80 pmoles cGMP formed/min/mg protein. Most of the vegetative activity is found in the supernatant of a 100,000 x g spin (S100). The enzyme is relatively unstable. It loses 40% of its activity after 3 hours storage on ice. Enzyme activity was measured from cells that had been shaken in phosphate buffer for various times. It was found that the specific activity changed little for at least 8 hours. Cyclic AMP at 10?4 M did not affect the guanylate cyclase activity from crude homogenates of vegetative or 6 hour phosphate-shaken cells. 相似文献
2.
The phosphorylation of troponin B by phosphorylase b kinase in skeletal muscle of mice carrying the phosphorylase b kinase deficiency gene 总被引:3,自引:0,他引:3
In skeletal muscle of animals with the phosphorylase kinase deficiency gene there is < 1% of the normal activity to convert phosphorylase to in the presence of Ca++, Mg++, and ATP (1). Correspondingly, there is < 1% of the normal activity to phosphorylate phosphorylase . Nevertheless, under the same conditions, these extracts catalyze the phosphorylation of troponin at a rate 57% of normal. Phosphorylase converting activity can be sedimented from skeletal muscle of control mice by centrifugation. This fraction isolated from I strain skeletal muscle extracts phosphorylates troponin at a rate 29–39% of the control. EGTA1 (15 mM) inhibits troponin phosphorylation by 50–60% in this fraction from both strains. The EGTA inhibition is reversed by 15 mM Ca++. Thus the phosphorylase kinase in skeletal muscle of animals with the phosphorylase kinase deficiency gene can phosphorylate troponin B, although it shows little or no activity with phosphorylase as a substrate. This observation is consistent with the normal muscle contractility of I strain animals. 相似文献
3.
A manganese-stimulated endonuclease from Bacillus subtilis 总被引:6,自引:0,他引:6
An endonuclease activity has been identified in extracts of . This activity is stimulated by Mn++ or Ca++ ions but not by Mg++ ions. The enzyme catalyzes the breakdown of native DNA of high molecular weight to fragments of molecular weights ranging from 3 × 106 to 20 × 106. A variety of DNA's from sources such as and T7 phage are attacked. About 61% of the activity of the cells is released into the medium during protoplast formation under conditions where 98% of the glucose 6-P dehydrogenase activity is retained by the cells. 相似文献
4.
1--Hexadecanoyl [U-14C]ethanediol can serve as substrate in the formation of 1--hexadecanoyl ethanediol 2-phosphorylcholine by particulate cell-free preparations from rat liver. Catalytic activity is largely associated with the microsomal fraction. The reaction requires CDPcholine and Mg++. Phosphatidylcholine cannot substitute for CDPcholine, but Mn++ is almost as effective as Mg++. Ca++ inhibits the reaction. The acyl ethanediol phosphorylcholine produced was identified by repeated cochromotography with authentic diol phospholipid to constant specific radioactivity, and by enzymatic and chemical degradations. 相似文献
5.
R Wierichs A Hagenmeyer H Bader 《Biochemical and biophysical research communications》1980,92(4):1124-1129
Vanadate inhibits the Ca++-ATPase of sarcoplasmic reticulum from pig heart half maximally at about 10?5 M. Mg++ promotes this inhibition by vanadate whereas increasing Ca++-concentrations protect the enzyme against vanadate inhibition. Keeping the ratio constant there was no influence of ATP on the vanadate inhibition at concentrations up to 5 × 10?3 M ATP. Whenever the ratio was higher than 1:1 the inhibitory effect of vanadate on the Ca++-ATPase was increased. 相似文献
6.
Michael D.P. Boyle 《Biochemical and biophysical research communications》1981,103(3):856-862
Zinc sulphate in the range of 10?4 to 2×10?5 M prevents the binding of to antigen antibody complexes, and the initation of the cascade of events in the classical complement pathway leading to cell lysis. Other heavy metals, Co++, Cd++, Cu++, or Mn++ were without effect in this concentration range. Zinc was ineffective when added after was bound and failed to displace which was already bound to antigen antibody complexes. The ability of zinc to regulate the binding of the zymogen or activated form of to antigen-antibody complexes represents a new method of controlling the initiation of the classical complement pathway. 相似文献
7.
Fumio Sawada Yasuhiko Miyauchi Hiroshi Tanaka Shinji Matsumoto 《Biochemical and biophysical research communications》1982,104(2):657-663
A novel method for the preparation of intact chromatin from the slime mold which retains the property of RNA synthesis is described. Preparations from G2-cells were highly active, while those from metaphase-cells were inactive. The plasmodial cells were disrupted by gentle homogenization on a polyethylene sieve in a neutral isotonic sucrose medium containing Mg++, deoxycholate and EGTA, a Ca++-chelating agent. The nuclei were lysed in a hypotonic buffer without use of EDTA and chromatin was precipitated by centrifugation after addition of Mg++. 相似文献
8.
T D Pollard E Eisenberg E D Korn W W Kielley 《Biochemical and biophysical research communications》1973,51(3):693-698
Troponin-tropomyosin is known to inhibit the Mg++ATPase activity of muscle actomyosin in the absence, but not in the presence, of Ca++. In contrast, we have now found that muscle troponin-tropomyosin inhibits the Mg++ATPase activity of muscle actin-activated myosin both in the presence and the absence of Ca++. Addition of purified tropomyosin and troponins-I, C and T demonstrated that it is troponin-T that acts differently in the two systems which differ only in the source of the myosin. These data suggest that myosin, as well as actin, plays a role in the troponin-tropomyosin control of muscle contraction and make it unlikely that control proteins identical to troponin-tropomyosin function in this amoeba. 相似文献
9.
R Simantov 《Life sciences》1978,23(25):2503-2508
Mouse pituitary tumor cells grown in tissue culture release endorphins spontaneously to the culture medium. Depolarization of these cells by incubation with high K+ concentration (56 mM) increased 2–3 folds the release of endorphins. The K+ evoked release was Ca++ dependent by that: , removal of Ca++ ions inhibited 90% of K+ stimulated release. , ethyleneglycol-bis (β-aminoethyl ether) N,N′-tetraacetic acid (EGTA) inhibited release of endorphins in the presence of high K+ and Ca++. It is suggested that dual regulatory system inhibit and/or stimulate release of endorphins from the pituitary glands. 相似文献
10.
Noncompetitive inhibition by substituted sulfonamides of dihydroorotase from Zymobacterium oroticum 总被引:3,自引:0,他引:3
Dihydroorotase from ss noncompetitively inhibited with respect to L-USA by a series of substituted sulfonamides which have the general structure, R1-SO2-NHR2. Values of Ki, determined from double reciprocal plots of 1/initial velocity versus 1/ [L-ureidosuccinate] are approximately 0.10 to 1.0 for the various sulfonamides tested. These data are compared to similar data for carbonic anhydrase which also requires either Zn++ or Co++ for catalytic activity. 相似文献
11.
A template independent poly (A)·poly (U) synthesizing activity has been isolated from . This activity is eluted from a DNA-cellulose column along with DNA-dependent RNA polymerase. The column fractions which exhibit this activity contain RNA polymerase holoenzyme plus a polypeptide which is slightly larger than sigma factor; pure RNA polymerase holoenzyme did not synthesize poly (A)·poly (U). The activity was dependent on the presence of ATP, UTP, and Mn++ (Mg++ could not substitute), and was inhibited by rifampicin, streptolydigin, and Cibacron Blue. The incorporation of nucleotides was not linear with time, but appeared after a lag period. The results suggest that a modified form of DNA-dependent RNA polymerase analogous to holoenzyme II is catalyzing the synthesis of poly (A)·poly (U). 相似文献
12.
Two forms of glutamine synthetase in free-living root-nodule bacteria. 总被引:23,自引:0,他引:23
Cell-free extracts of 61A76 contain two forms of glutamine synthetase (EC 6.3.1.2) which can be easily separated by isoelectric focusing. The more acid form (pI = 5.4), like the enzyme from , is stable at 50° and catalyses an ADP-dependent transferase reaction, whose inhibition by excess Mg++ can be relieved by snake venom phosphodiesterase. The more alkaline form (pI = 6.1) is labile at 50°, and catalyses and ADP-dependent transferase reaction which is strongly inhibited by Mg++ regardless of phosphodiesterase treatment. We have also observed the two forms of the enzyme in a nitrogenaseless mutant of 61A76, and in other strains of rhizobia, but only the acid form in W, OP, and M 51A. 相似文献
13.
2,6-dibromothymoquinone (DBMIB) and other coenzyme Q analogs partially inhibit electron transport and the membrane-bound Mg++ stimulated ATPase of membranes. The inhibitions by DBMIB are fully reversed by coenzyme Q6, and other analogs show partial reversal by coenzyme Q6. Electron transport reactions inhibited are NADH and lactate oxidase, NADH menadione reductase, lactate phenazinemethosulfate reductase and duroquinol oxidase. The concentrations of DBMIB required are similar for electron transport and ATPase inhibition and inhibitions are all increased by uncouplers. Electron transport and ATPase are not inhibited in a DBMIB insensitive mutant. Soluble ATPase extracted from the membranes does not show DBMIB inhibition under either high or low Mg++ conditions. Lipophilic chelators show additional inhibition over DBMIB. It appears that coenzyme Q functions at three sites in electron transport where ATPase activity is controlled. Coenzyme Q deficient mutants also show decreased electron transport and ATPase activity which is restored by coenzyme Q. 相似文献
14.
Synthesis of simian virus 40 DNA in isolated nuclei 总被引:1,自引:0,他引:1
P K Qasba 《Biochemical and biophysical research communications》1974,60(4):1338-1344
The presence or absence of calcium ions during the isolation of nuclei from SV40-infected African green monkey kidney cells significantly affects the size of SV40 DNA synthesized . When Ca++ is present during the nuclear isolation procedure, the 3–7S fragments of SV40 DNA synthesized mature into long chains; in the absence of Ca++ they do not. 相似文献
15.
When young intact forespores of Bacillus megaterium were incubated with either Mn++ or the ionophore X-537A, the pool of 3-phosphoglyceric acid (3-PGA) was stable. However, incubation of forespores with Mn++ plus the ionophore X-537A resulted in rapid and complete utilization of the 3-PGA. This effect was not seen with Ca++ or Mg++, and was also not observed with older forespores or fresh dormant spores. Since the phosphoglycerate mutase of has an absolute and specific requirement for Mn++, it is possible that phosphoglycerate mutase in developing forespores may be inactive because of a low intrasporal level of free Mn++. 相似文献
16.
Steven D. Schimmel Thomas Hallam 《Biochemical and biophysical research communications》1980,92(2):624-630
The tumor promoter phorbol 12-myristate 13-acetate rapidly induces alterations in both Ca++ content and transport in cultured differentiated chick myoblasts. At 4 ng/ml (6nM), the promoter caused a 25 ± 12% decrease in total intracellular Ca++ within 5 h after its addition. Measurement of 45Ca++ transport at this time revealed a 15 ± 6% decrease in the rate constants for both efflux and influx. Values of for the cytosolic Ca++ pool in control and treated cells were 9.1 and 10.7 min, respectively, for efflux and 8.6 and 10.4 min, respectively, for influx. Ca++ influx was decreased maximally within 90 sec after promoter addition. No effect was observed on 86Rb+ uptake or intracellular concentration at equilibrium. The Ca++ response is among the most rapid yet reported and may play a primary role in altering cellular metabolism. 相似文献
17.
M Mason 《Biochemical and biophysical research communications》1974,60(1):64-69
At pH 6.4, rat kidney mitochondrial kynurenine aminotransferase activity is enhanced several-fold by the addition of CaCl2, apparently because Ca++ facilitates the translocation of α-ketoglutarate, one of the substrates, across the mitochondrial inner membrane. Chloride salts or Mg++, Mn++, Na+, K+, and NH4+ did not have this effect. At pH 6.8, the enzyme activity was near maximal even without added Ca++ but was strongly depressed by either of two calcium chelating agents, quinolinic acid (Q.A.) and ethyleneglycol-bis(β-aminoethyl ether)N,N′-tetraacetic acid (EGTA). These observations support the view that Ca++ is involved in regulating kidney mitochondrial translocation of α-ketoglutarate and that the reported interference of polycarboxylate anion translocation by Q.A. depends on the ability of that agent to chelate Ca++. 相似文献
18.
J Wiegel 《Biochemical and biophysical research communications》1978,82(3):907-912
The α-isopropylmalate synthase (EC 4.1.3.12) from was inactivated by EDTA in a time-dependent reaction. Only the addition of Mn++ plus dithiothreitol could restore the activity. The substrate, α-ketoisovalerate, prevented the inactivation; the feedback inhibitor, leucine, and it's antagonist, valine, increased the rate of inactivation. Except for α,α′-bipyridyl, chelating reagents, other than EDTA had no effect on the enzyme stability. It is suggested that the α-isopropylmalate synthase is a metallo enzyme - the evidence points to Mn++ as the metal ion - and that this enzyme uses a mechanism of catalysis which differs from that of the analogous malate synthase (EC 4.1.3.2) and citrate synthase (EC 4.1.3.4). 相似文献
19.
E.coli endotoxin stimulates endogenous lipolysis in the perfused rat heart. Verapamil® inhibits endotoxin- (as well as glucagon-) stimulated lipolysis. This suggests that the endotoxin used increases the availability of Ca++ to the lipolytic system in the cardiocytes. This conclusion is supported by the observed stimulation of contractility of the heart, especially during perfusion at a low Ca++ concentration.The endotoxin was found to inhibit ATP-dependent Ca++ accumulation in sarcolemma vesicles prepared from rat heart. A direct Ca++ ionophoric action of the endotoxin on these vesicles could be excluded.It is discussed that Ca++ overload may not be confined to the cardiovascular system during endotoxemia. 相似文献
20.
Chelation of divalent cations by lomofungin: role in inhibition of nucleic acid synthesis 总被引:3,自引:0,他引:3
K Pavletich S C Kuo J O Lampen 《Biochemical and biophysical research communications》1974,60(3):942-950
Lomofungin inhibition of yeast growth and RNA synthesis is prevented by Cu++ or Zn++ ions which chelate with the antibiotic and prevent its uptake by the cells. EDTA potentiates the inhibition. Mg++ ions do not protect or against the inhibition of purified bacterial RNA and DNA polymerases. Lomofungin prevents formation of the RNA polymerase. DNA initiation complex, probably by chelation with the firmly bound Zn++ of the enzyme. 相似文献