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At least 127 records · Page 7Linked to original sources
PubMed1983

Metabolism of zinc and copper in the neonate: zinc thionein in developing rat brain, heart, lung, spleen, and thymus.

In a continuing study of the importance of metallothionein (MT) in the growth and development of neonates, zinc and copper metabolism in rat brain, heart, lung, spleen, and thymus has been analyzed in 5, 10, 15, 20, and 25 day old rats. Total, cytosol, and MT zinc and copper concentrations and organ contents were determined. Zinc, but very little, if any copper was associated with MT in these organs. Concentrations ranged from 0.03 to 3.3 micrograms Zn in MT/g; organ contents ranged from 0.003 to 2.2 micrograms Zn in MT/organ. Brain exhibited the highest concentrations and contents of zinc in MT, approaching the levels found in kidneys. Rank order of organ contents of zinc in MT was brain greater than lung greater than heart, spleen, thymus, during this neonatal growth period. When organ growth was rapid, a large percentage (20-95%) of the cytosolic zinc present in these organs was associated with MT, as has been previously observed with liver, kidneys, and testes. None of these organs undergoes the dramatic changes in zinc and copper metabolism previously observed in neonatal rat liver and gastrointestinal tract, and in maturing testes. They are more comparable to kidneys in their concentrations of zinc in MT. Like testes, little copper is found in these organs.

Animals↗
PubMed1986

Determination of Cd-thionein in biological materials: comparative standard recovery by five current methods using protein nitrogen for standard calibration.

Five methods of metallothionein (MT) estimation in biological materials (Hg-saturation assay, Cd-saturation assay, thiolate group determination, Sephadex G-75 gel chromatography with subsequent Cd determination by Zeeman-AAS, and a radioimmunoassay (RIA) were compared for their ability to recover standard MT(rabbit Cd-MTI) from liver or kidney S9. Uniform molar calibration of all assays was achieved using the known amino acid composition of standard MT and the nitrogen content of the standard MT stock solution as measured after complete Kjeldahl digestion. Known molar amounts of standard MT were added exogenously to rat liver- or kidney-S9 samples and recoveries measured using the methods indicated. In an overall rating, RIA and Cd-saturation assay performed best with recoveries of 97 +/- 12.0 and 105 +/- 9.7%, respectively. On the other hand, the remaining methods either underestimated (thiolate group determination, G-75/Cd-AAS) or overestimated (Hg-saturation assay) the theoretical expectation by up to 44%.

Animals↗
PubMed1985

Isolation and partial characterization of a non-thionein, zinc-binding protein from the liver of rainbow trout (Salmo gairdneri).

A Zn-binding protein (ZBP) was induced in the liver of Donaldson strain rainbow trout by 7 mg/kg i.p. injections of divalent Zn ions. ZBP synthesis was inhibited (74%) by cycloheximide. ZBP had a minimum molecular weight of 16,900 and was composed of two subunits with apparent molecular weights of 9650 and 6050. Purified ZBP contained 4% phenylalanine, 4% isoleucine, 5-6% leucine and 3.48% Zn. Each protein molecule bound nine Zn atoms and contained at least four sulfhydryl groups. Molecular weight, two subunits and the presence of aromatic amino acids suggested that ZBP was not metallothionein.

Amino Acids↗
PubMed2004

A differential assay for the reduced and oxidized states of metallothionein and thionein.

In the cellular environment, the sulfur ligands in zinc/thiolate coordination sites of proteins can be oxidized with concomitant mobilization of zinc. The characterization of such "redox zinc switches" requires the determination of three species, i.e., the zinc-containing complex and the zinc-free complex with the thiolate ligands either reduced or oxidized. Differential chemical modification of thiol groups in the presence and absence of either reducing or chelating agents allows the analytical speciation of such systems as demonstrated here for the characterization of the redox and metal-binding states of mammalian metallothionein. Thiol derivatization with 6-iodoacetamidofluorescein in the presence and absence of the reducing agent tris(2-carboxyethyl)phosphine, high-performance liquid chromatographic separation, and photometric detection are employed to determine the reduced and oxidized protein. Because the holoprotein reacts only in the presence of a chelating agent such as ethylenediaminetetraacetate (EDTA) its amount can be determined as the difference between measurements in the presence and the absence of EDTA. This method is applied to the study of the chemical and enzymatic oxidation of metallothionein/thionein. It should also greatly facilitate the characterization of the redox and metal-binding properties of zinc/thiolate coordination environments of other proteins such as zinc finger proteins.

Animals↗
PubMedDate not supplied

Evidence of a cadmium-thionein and the glycine cleavage system in Oxytricha granulifera.

This work presents the further purification of a Cd-linking protein in Oxytricha granulifera by reverse-phase chromatography. This protein contains 25% cysteine and no aromatic amino acid. It may be considered as a chelatin with some similarity to metallothioneins. During the purification of another Cd-linking compound, we were able to demonstrate that the H protein precursor of glycine cleavage is present in Oxytricha. This is the first finding of the presence of this system in Protozoa.

Amino Acid Sequence↗
PubMed1990

Hippocampal zinc thionein and pyridoxal phosphate modulate synaptic functions.

The hippocampus, a component of the limbic system, is a prominent subcortical structure, which not only contains high concentrations of zinc, but also exhibits regional variations in this essential element, with concentrations being highest in the hilar region and lowest in the fimbria. For example, the concentration of zinc in the mossy fiber axons has been estimated to approach 300-350 microM. Both zinc and pyridoxal phosphate (PLP) deficiency and excess have been reported to produce epileptiform seizures, which are blocked by gamma-aminobutyric acid (GABA). The proposed mechanism is that at physiological concentrations zinc stimulates the activity of the hippocampal pyridoxal kinase (50% stimulation at 1.7 x 10(-7) M), enhancing the formation of PLP, whereas in pharmacological doses zinc inhibits the activity of glutamate decarboxylase (GAD) directly (50% inhibition at 6.5 X 10(-4) M) by preventing the binding of PLP to HoloGAD. Furthermore, recent studies have shown that two forms of GAD are found in the rat brain. One form (GAD A) does not require PLP for maximal activity, while another form (GAD B) does. Furthermore, the ratio between GAD A and GAD B is nonuniform throughout brain areas, and the hippocampus contains twice as much GAD B (the PLP-requiring GAD) as GAD A. Although the hippocampus is a common target of exogenous neurotoxic agents, "free" zinc in greater than physiological concentrations should be considered an endogenous central neurotoxin. For example, iontophoretically applied zinc in the frontoparietal cortex enhances and prolongs the firing rate of neurons in urethane-anesthetized rat. In addition, zinc (50-500 microM) significantly depresses the paired-pulse potentation in the hippocampal CA3 subfield. Moreover, zinc selectively blocks the action of N-methyl-D-aspartate on cortical neurons and enhances the quisqualate receptor-mediated injury. Finally zinc competitively inhibits the calcium-dependent release of transmitter by inhibiting the entry of Ca2+ into the nerve terminals. Since zinc in a concentration of 300-350 microM could not possibly remain "unbound" in the hippocampus, we searched for and identified a metallothionein-like protein (MT) in the bovine hippocampus, which produces two isoforms on reverse-phase HPLC and lacks aromatic amino acids, but possesses metallomercaptide bonds. We believe that the hippocampal metallothionein, by donating zinc to an extensive number of zinc-activated, PLP-mediated biochemical reactions, modulates synaptic functions. Furthermore, by virtue of its inducibility, metallothionein binds additional amounts of zinc, maintains its steady-state concentration, prevents inhibition of an extensive number of sulfhydryl-containing enzymes and receptor sites, and hence averts metal-related neurotoxicity.

Animals↗
PubMed1985

Thymus metallothionein: regulation of zinc-thionein in the aging mouse.

The presence of a zinc-inducible metallothionein in mouse thymus tissue has been shown, together with an age-related modulation of zinc, metallothionein, and thymus mass. Metallothionein (MT) and zinc concentrations were found to be maximum prior to completion of thymic growth and to be at a minimum when development of the thymus had ceased. Subsequent transient outgrowths of the thymus during involution showed similar associated fluctuations of MT and zinc levels. A marked difference in the latter parameters was found on comparison with New Zealand Black mice known for development of early onset autoimmunities. These findings provide a new avenue for both investigation of the regulation of zinc in thymus tissue, as well as the possible elucidation of the molecular basis for certain age-related immune dysfunctions.

Aging↗