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41.
Purification and comparative properties of microsomal and glyoxysomal malate synthase from castor bean endosperm 总被引:7,自引:5,他引:2
Sucrose density gradient centrifugation was employed to separate microsomes, mitochondria, and glyoxysomes from homogenates prepared from castor bean (Ricinus communis) endosperm. In the case of tissue removed from young seedlings, a significant proportion of the characteristic glyoxysomal enzyme malate synthase was recovered in the microsomal fraction. Malate synthase was purified from both isolated microsomes and glyoxysomes by a procedure involving osmotic shock, KCI solubilization, and sucrose density gradient centrifugation. All physical and catalytic properties examined were identical for the enzyme isolated from both organelle fractions. These properties include a molecular weight of 575,000, with a single subunit type of molecular weight 64,000, a pH optimum of 8, apparent Km for acetyl-CoA of 10 μm and glyoxylate of 2 mm. Microsomal and glyoxysomal malate synthases showed identical responses to various inhibitors. Adenine nucleotides were competitive inhibitors with respect to acetyl-CoA, and oxalate (Ki 110 μm) and glycolate (Ki 150 μm) were competitive inhibitors with respect to glyoxylate. Antiserum raised in rabbits against purified glyoxysomal malate synthase was used to confirm serological identity between the microsomal and glyoxysomal enzymes, and was capable of specifically precipitating 35S-labeled malate synthase from KCI extracts of both microsomes and glyoxysomes isolated from [35S]methionine-labeled endosperm tissue. 相似文献
42.
Saline incubation extracts of mature erythrocytes were assayed in vivo by a variety of techniques in order to study their ability to modify the proliferation of maturing erythroid cells. Using comparable extracts from granulocytes and lymphocytes, the specificity of the effect of the red cell extract for erythroid cells was confirmed by measurement of autoradiographic labelling indices, radio-iron incorporation and spleen colony growth. The erythroid cells were found to be very sensitive to the effects of the extract, as little as 10 μg per mouse producing a maximum effect on iron incorporation. It was found that the extract does not block erythroid cell proliferation completely but simply lengthens the cell cycle, mainly by increasing the G1 phase of the cycle. There was no effect on the committed erythroid precursor cells. The in vivo activity, specificity and non-toxicity to the cells, together with the cells' sensitivity to red cell extract suggest, therefore, that this inhibitor may play a physiological role in the control of red cell production. 相似文献
43.
J M Lord S I White C J Bailey T W Atkins R F Fletcher K G Taylor 《BMJ (Clinical research ed.)》1983,286(6368):830-831
To investigate the effect of metformin on insulin receptor binding and diabetic control, eight obese type II diabetic patients were studied before treatment, after one and four weeks of taking metformin (500 mg thrice daily), and four weeks after withdrawal of the drug. After one and four weeks of treatment the number of erythrocyte insulin receptors had increased by 116% and 184% respectively. This was due almost entirely to an increase in the number of low affinity binding sites. The number of receptors was still raised four weeks after metformin had been withdrawn. Diabetic control as assessed by urinary glucose, glycosylated haemoglobin (HbA1), and glucose tolerance values was significantly improved during metformin treatment, while plasma insulin concentrations were not altered. These results indicate that metformin produces a rapid and protracted increase in low affinity insulin receptors in type II diabetes, associated with greater insulin sensitivity and improved diabetic control. 相似文献
44.
45.
The rRNA N-glycosidase activities of the catalytically active A chains of the heterodimeric ribosome inactivating proteins (RIPs) ricin and abrin, the single-chain RIPs dianthin 30, dianthin 32, and the leaf and seed forms of pokeweed antiviral protein (PAP) were assayed on E. coli ribosomes. All of the single-chain RIPs were active on E. coli ribosomes as judged by the release of a 243 nucleotide fragment from the 3′ end of 23S rRNA following aniline treatment of the RNA. In contrast, E. coli ribosomes were refractory to the A chains of ricin and abrin. The position of the modification of 23S rRNA by dianthin 32 was determined by primer extension and found to be A2660, which lies in a sequence that is highly conserved in all species. 相似文献
46.
47.
Addition of an ER retention signal to the ricin A chain increases the cytotoxicity of the holotoxin. 总被引:4,自引:0,他引:4
With the exception of diphtheria toxin, which translocates from acidified endosomes, the intracellular organelle from which the catalytic moieties of several plant and bacterial toxins enter the target cell during endocytic uptake has not been identified. We have recently proposed that some toxins may travel the entire secretory pathway in reverse, moving from the cell surface to the lumen of the ER, before entering the cytosol. Several bacterial toxins have the ER retention sequence KDEL or a related analogue at their carboxyl termini, suggesting that the KDEL receptor may play a role in delivering these toxins to the ER. Here we provide further support for this possibility since the cytotoxicity of ricin, which lacks a KDEL sequence, can be significantly increased by adding KDEL to the C-terminus of its A chain. 相似文献
48.
T Hasunuma H Tsubota M Watanabe Z W Chen C I Lord L C Burkly J F Daley N L Letvin 《Journal of immunology (Baltimore, Md. : 1950)》1992,148(6):1841-1846
Cell surface-expressed CD4 binds to the envelope glycoprotein of HIV-1 and mediates syncytia formation through interacting with membrane expressed HIV-1 gp120. Further possible roles of the CD4 molecule in the process of cell infection by HIV-1 remain poorly understood. In our study we describe two mAb that recognize the V3/V4 domain of the CD4 molecule. Although these mAb do not inhibit gp120-CD4 binding or HIV-1-induced syncytia formation, they inhibit HIV-1 infection of human PBL. These findings suggest that discrete, definable domains of the CD4 molecule may be involved in interactions after HIV-1 envelope binding that lead to virus entry into the cell. 相似文献
49.
We have devised a rapid method for examining the expression of a toxin gene following in vitro transfection using a bacterial beta-galactosidase (lacZ) gene as a reporter gene. Ricin A chain DNA and the lacZ gene, both under the control of the immunoglobulin gene promoter and enhancer, were transfected into mouse fibroblast cells (L cells). Transient expression of the lacZ gene was detected 2 days after transfection by histochemical staining of the transfectants with 5-bromo-3-indolyl-beta-D-galactoside. Cotransfection of the ricin A chain gene resulted in a progressive reduction in the number of lacZ transfectants as the expressed toxin killed the cells. A ricin construct with the intervening sequence from the human beta-actin gene required 4 days instead of 2 days to produce the toxic effect. This is a useful method for examining the expression of toxin gene in a cell. 相似文献
50.
D. Denis S. Charleson A. Rackham T.R. Jones A.W. Ford-Hutchinson A. Lord M. Cirino Y. Girard M. Larue J. Rokach 《Prostaglandins & other lipid mediators》1982,24(6):801-814
Leukotriene F4 (LTF4 and LTF4 sulfone have been synthesized and their biological activities determined in the guinea pig.
LFT4 displayed comparable activity to LTD4 on guinea pig trachea and parenchyma but was less active on the ileum. When injected intravenously into the guinea pig, LTF4 induced a bronchoconstriction (ED50 16 μg Kg−1) which was blocked by indomethacin and FPL-55712 and was 50–100 X less potent than LTD4 in this assay. LTF4 sulfone was approximately 2–5 times less active than LTF4
and
. When injected into guinea pig skin with PGE2 (100 ng); LTF4 and LTF4 sulfone (10–1000 ng) induced changes in vascular permeability. The order of potency in this assay was LTE4 sulfone = LTD4 = LTD4 sulfone > LTE4 > LTF4 = LTF4 sulfone. 相似文献