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At least 577 records · Page 32Linked to original sources
PubMed1985

Homogeneous bivalent insulin receptor: purification using insulin coupled to 1,1'-carbonyldiimidazole activated-agarose.

A novel affinity gel, consisting of insulin coupled to 1,1'-carbonyldiimidazole-activated agarose (CDI-agarose), was used to purify insulin receptors from human placenta to homogeneity. This affinity gel is reproducibly prepared and is reported to have a number of advantages over the standard cyanogen bromide activated supports, such as ease and simplicity of coupling and minimal ligand leakage and non-specific binding. Insulin receptors in Triton X-100-solubilized microsomal membranes were purified 2,000-fold by sequential affinity chromatography on wheat germ lectin-agarose and insulin-CDI-activated agarose. They have one of the highest specific insulin-binding capacities (6 nmol/mg protein) reported and can be calculated to have a binding valence of two on the basis that the molecular weight of the oligomeric receptor is 300-350,000.

Chromatography, Affinity↗
PubMed1980

The interaction of cadium-induced rat renal metallothionein with bivalent mercury in vitro.

Addition of Hg2+ in vitro to metallothionein (Cd : Cu : Zn = 6.5 : 4 : 1) from the kidneys of Cd2+ exposed rats appears to result initially in the replacement of Zn2+, then Cd2+ and finally copper. The ionic stoichiometries between Hg2+-binding and the release of Cd2+ (or Zn2+) and copper are 3 : 2 and 1 : 1 respectively. After treatment with amounts of Hg2+ sufficient to displace completely either the bound Zn2+ and Cd2+, or all of the original cations, the metallothionein has little or no negative charge at pH 8.0 and is not resolved into the two isometallothioneins, which characterize the (Cd, Cu, Zn)-thionein, by ion exchange chromatography at this pH. Cation substitution occurs in both isometallothioneins and there is no evidence that Hg2+ interacts preferentially with one of them. Treatment of the metallothionein with increasing amounts of Hg2+, equivalent to approx. 25% and 50% of the bound cations gives rise to a range of molecular species of progressively decreasing negative charge. The consistent stiochiometry between Hg2+ uptake and Cd2+ or Zn2+ release at all concentrations of Hg2+ indicates that free thiol groups are not formed during the substitution reaction.

Animals↗
PubMed1984

Testosterone metabolism by homogenates of human prostates with benign hyperplasia: effects of zinc, cadmium and other bivalent cations.

The effects of various quantities of Ba, Be, Ca, Cd, Co, Cu, Mg, Mn, Sr, Zn and EDTA on the formation of 5 alpha-reduced metabolites of testosterone (T) substrate and of 3 alpha-/3 beta-reduced metabolites of 5 alpha-dihydrotestosterone substrates by homogenates of 6 human hyperplastic prostate glands were studied in incubations at pH 7.4 with NADPH-generating system. Effects of these cations and EDTA on the VM and KM of the 5 alpha-reductase and 3 alpha-/3 beta-hydroxysteroid dehydrogenases (-HSD) were also measured. Quantities of 5 alpha-reduced T metabolites were significantly increased by Cd, Cu and Zn supplementations. These increments were shown to result from significant augmentations of the VM but no change in KM of the NADPH-dependent 5 alpha-reductase. Quantities of 3 alpha-reduced DHT metabolites were significantly decreased by Cd and Cu supplementations and resulted from an increase of the KM of the NADPH-dependent 3 alpha-HSD by Cd and both an increase of KM and a decrease of VM by Cu. Quantities of 3 beta-reduced DHT metabolites were significantly decreased by Cd and Cu supplementations. Increase of the KM of the NADPH-dependent 3 beta-HSD by Cd was found significant while Cu both increased the KM and decreased the VM of the enzyme. EDTA-related changes in 5 alpha-reductase activity were shown to result from the EDTA-induced decrease of the pH of the medium. No effect of EDTA was observed on the activities of both 3 alpha/3 beta-HSD.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗