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51.
D G Warnock W C Yang Z Q Huang E J Cragoe 《The Journal of biological chemistry》1988,263(15):7216-7221
Amiloride is a reversible inhibitor of the Na+/H+ antiporter which acts at the external aspect of the transport system. The kinetics of inhibition of the Na+/H+ antiporter with amiloride have been controversial, with the usual finding of simple competitive inhibition, but with other reports of mixed and noncompetitive inhibition of the transporter by amiloride. The present experiments demonstrate that the chloride content of the external transport buffer affects the kinetics of amiloride inhibition. Either simple competitive or mixed inhibition by amiloride was observed in the same vesicle preparations depending on the presence of chloride or gluconate in the buffer. The effect of chloride on the inhibitory effect of amiloride was dependent on the concentration of chloride and amiloride. Similar effects were observed with more potent analogues of amiloride. These findings suggest that the external aspect of the antiporter has a site or sites at which the inhibitory effects of amiloride on the Na+/H+ antiporter can be modified by chloride, even though chloride has only slight effects on the kinetics of the Na+/H+ antiporter in the absence of amiloride. 相似文献
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55.
A new method for the assay of glutaminase activity: direct measurement of product formation by an ammonia electrode 总被引:1,自引:0,他引:1
Y Z Huang 《Analytical biochemistry》1974,61(2):464-470
A simple, reliable procedure is described for the quantitative assay of glutaminase reaction by measuring product formation using an ammonia electrode. The ammonia electrode is a gas-detecting electrode, sensing the level of dissolved ammonia in aqueous solutions. Ammonia concentration can be read from calibration curves after converting ammonium ion to ammonia by adding sufficient base. Sample color and turbidity do not affect measurements, and samples need not be distilled. The concentrations of the three glutaminase isoenzymes from rat tissues measured by this method are strictly comparable to those measured by other methods. 相似文献
56.
Pyruvate decarboxylase (PDC, EC 4.1.1.1) is a thiamin diphosphate-dependent enzyme about which there is a large body of structural and functional information. The active site contains several absolutely conserved ionizable groups and all of these appear to be important, as judged by the fact that mutation diminishes or abolishes catalytic activity. Previously we have shown [Schenk, G., Leeper, F.J., England, R., Nixon, P.F. & Duggleby, R.G. (1997) Eur. J. Biochem. 248, 63-71] that the activity is pH-dependent due to changes in kcat/Km while kcat itself is unaffected by pH. The effect on kcat/Km is determined by a group with a pKa of 6.45; the identity of this group has not been determined, although H113 is a possible candidate. Here we mutate five crucial residues in the active site with ionizable side-chains (D27, E50, H113, H114 and E473) in turn, to residues that are nonionizable or should have a substantially altered pKa. Each protein was purified and characterized kinetically. Unexpectedly, the pH-dependence of kcat/Km is largely unaffected in all mutants, ruling out the possibility that any of these five residues is responsible for the observed pKa of 6.45. We conjecture that the kcat/Km profile reflects the protonation of an alcoholate anion intermediate of the catalytic cycle. 相似文献
57.
Kuo Huang Ling Bai Jiun Chen Yun Wen Peng Shih Chong Tsai Fu Chuo Peng Chung Kuang Yang 《Mycotoxin Research》1987,3(2):58-64
The chemical reaction of cleavaging territrem B to give 3,4,5-trimethoxy benzoic acid by alkaline hydrogen peroxide was investigated. The method was applied for confirmation of the chemical structure of the aromatic moiety of territrem A, A’, B, and B’. The physicochemical properties of the aromatic cleavage product of territrem Aindicated the structure as 3,4-methylendioxy, 5-methoxy benzoic acid (or 4-methoxy, 6-carboxy, 1, 3-benzodioxole). The experiment also gave the evidences that territrem A and A’, on the other hand territrem B and B’ have the identical aromatic moieties on their structures. 相似文献
58.
用云南山楂(Crataegus scabrifolia(Franch.)Rehd.)成年树茎尖和实生芽两种不同发育阶段的材料为外殖体,诱导它们休眠芽萌动,丛生芽条并诱导芽条生根。实验结果如下:1.以成年态的云南山楂侧芽为外植体,培养在附加IAA 0.1—0.5mg/l+6-BA 1-2mg/l的MS培养基上可诱导芽的萌发;将芽继代培养在附加0.5—1mg/l 6-BA的SH或MS培养基上,40天后芽数增殖4—6倍;将芽条截下置于1/2MS培养基上,附加不同浓度的IAA或IBA,可得到50—80%的生根率。2.以实生芽为外殖体,在相同条件下,则20天后芽数增殖便可获4—6倍;98%以上生根。结果表明:云南山楂的幼年态要比成年态易脱分化和再分化。 相似文献
59.
新疆绿蟾蜍的染色体组型初步研究 总被引:2,自引:2,他引:0
近年来,有关两栖类的染色体组型已有不少报道。无尾两栖类中蜍蟾属(Bufo)的染色体数目分为两类:2n=22和2n=20(Blain,1972)。我们对采自新疆4个地区的绿蟾蜍进行了染色体组型分析,发现其二倍体细胞染色体数均为44,是四倍体。现将我们的初步研究报道如下。 相似文献
60.
Protein kinase C-dependent and -independent pathways of proto-oncogene induction in human astrocytoma cells 总被引:8,自引:0,他引:8
P J Blackshear D J Stumpo J K Huang R A Nemenoff D H Spach 《The Journal of biological chemistry》1987,262(16):7774-7781
We compared the abilities of the muscarinic agonist carbachol, epidermal growth factor (EGF), and phorbol 12-myristate 13-acetate (PMA) to induce proto-oncogene mRNA accumulation and other cellular responses in normal and protein kinase C-deficient 1321-N1 human astrocytoma cells. PMA, carbachol, and EGF all stimulated rapid accumulation of mRNA for the proto-oncogenes c-fos and c-myc in the normal cells; in the protein kinase C-deficient cells, carbachol and EGF, but not PMA, retained this effect, which was not mimicked by the calcium ionophore A23187. Both carbachol and PMA activated protein kinase C in these cells, as evidenced by the stimulated phosphorylation of an acidic Mr 80,000 protein kinase C substrate protein with phosphoamino acid and peptide map identity. This response was mimicked by several other neurotransmitters in these cells, including epinephrine, histamine, oxotremorine, and serotonin, and was abolished in cells made protein kinase C-deficient by preincubation with high concentrations of PMA. Both PMA and carbachol promoted the phosphorylation of the ribosomal protein S6 and activated an S6 protein kinase in the normal but not in the protein kinase C-deficient cells. EGF, in contrast, did not appear to activate protein kinase C, but promoted the phosphorylation of S6 and activation of the S6 kinase in both normal and protein kinase C-deficient cells. We conclude that, in 1321-N1 cells, induction of c-fos and c-myc mRNA can occur through a protein kinase C-dependent pathway and one or more independent pathways, exemplified by the responses to carbachol and EGF in the protein kinase C-deficient cells. 相似文献