Biomedical subjects
Publications and source records attributed to D M Templeton.
Attempts to crosslink metallothionein through lysine residues have resulted in trapping of octameric structures. Two such polymers have been characterized. They are of a critical size for glomerular filtration, and unique tissue distributions of cadmium arise when they are injected into rats.
Various approaches to promote the one-electron transfer reaction of lipoamide dehydrogenase have been investigated. An addition of riboflavin facilitates the electron transfer between NADH and Fe(CN) 3-/6. Aminocarboxymethylation and cadmium derivatization of the catalytic disulfide moderately activate the electron transfer reaction. An enhancement in the electron transferase activity of the Co(II)-enzyme complex is associated with decreased Michaelis and inhibition constants. Phosphopyridoxamidation identifies the suppressive effect on the electron transferase activity of carboxyl groups proximal to the catalytic histidine residue of lipoamide dehydrogenase. Amidation of these carboxyl groups with diamine greatly promote the one-electron transfer reaction. The increased electron transferase activity of the amidated enzyme is related to the charge nature of the amidated nucleophile and associated with the increased catalytic efficiency which undergoes a shift in the pH profile. The introduction of cationic aminoethyl groups presumably encourages the formation of an anionic flavosemiquinone which promotes the one-electron transfer reaction.
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The magnetic circular dichroic (MCD) spectra of oxidized and reduced flavins are recorded in various solvents. They are shown to be sensitive to flavin environment. The MCD spectra of oxidized and reduced lipoamide dehydrogenase are reported. In the oxidized enzyme the sign of the B term associated with the 27 000-cm-1 band is reversed from free flavins. This is attributed to interaction of the disulfide with the short-axis dipole of FAD. The sign reversal is also present in a closely related disulfide enzyme, glutathione reductase, but absent in glucose oxidase. In the half-reduced enzyme, the appearance of an A term at 18 180 cm-1 is attributable to a charge-transfer complex with a thiolate anion as donor. Insensitivity of the term's energy and intensity to the redox state of flavin suggests that a protein residue may accept or stabilize the thiolate charge transfer.
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The accumulation of hepatic and renal Cd, Zn, Cu, and metallothionein (MT) was investigated in ringed turtle doves (Streptopelia risoria) chronically exposed to 3 different concentrations of dietary Cd. When only tissue-Cd was considered as an inducer of MT, kidney was found to be 35% as responsive as liver in producing MT. However, when all potentially relevant inducing metals (Cd + Zn + Cu) were taken into account, kidney was found to be 85% as responsive as liver. The greater production of MT/mol Cd in liver was accounted for mainly by a greater co-accumulation of Zn/mol Cd in liver than in kidney. We conclude that the apparent tissue specificity in expression of MT may be overestimated by failure to consider fluctuations in multiple inducers. Variability in tissue-MT concentrations after chronic dietary Cd administration is best accounted for by a consideration of tissue-Cd, -Zn, and -Cu, rather than tissue-Cd alone.
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Previous studies have indicated altered rates of sulfate clearance in experimental diabetes, but have disagreed on the magnitude and direction of change of serum sulfate, or its impact on tissue sulfate concentrations. The present study was undertaken in order to investigate the temporal effects of streptozotocin-induced diabetes on sulfate pools in the rat. In contrast to some earlier reports, we found no effects of diabetes on serum sulfate concentrations throughout 12 weeks of disease, as measured by ion chromatography. However, marked increases in sulfate concentration were found in liver cytosol (3.5-fold; p less than 0.0005) and kidney (1.7-fold; p = 0.002) by 7 weeks. The measurement of inulin space demonstrated that the changes in hepatic sulfate were due to increased concentrations of the ion in the cell cytosol. Normal serum sulfate concentrations, together with reports of increased renal clearance of sulfate in diabetes, suggest an intracellular origin of the excess cytosolic sulfate. Glucose did not affect the uptake of sulfate by renal mesangial cells in culture. These aberrations in sulfate metabolism are not such as to compromise biological sulfation reactions, and cannot account for reported changes in the incorporation of sulfate into basement membrane proteoglycans during diabetes.
Thalassemic patients with iron overload are presently treated with deferoxamine or the experimental chelator deferiprone. To understand how these agents remove iron from the liver, cultured human hepatoma cells loaded with iron were previously used as a model for hepatic iron overload. The present study was undertaken to characterize further the pathways of iron transport and distribution in these cells. The activation energy for Fe2+ transport is 19 kJ/mol greater than for Fe3+, and the rate of Fe2+ transport--but not that of Fe3(+)--decreases with temperature above 25 degrees C, suggesting distinct uptake processes for different redox states of iron. Iron loading, which promotes a greater rate of Fe3+ transport, also caused a proportionally greater deposition of iron in the microsomal and cytosolic compartments and specifically lowered the activities of succinate-cytochrome c reductase and 5'-nucleotidase, representative markers of the mitochondria and plasma membrane, respectively. Both deferiprone and deferoxamine decreased total cellular iron and iron in each fraction except cytosol, indicating mobilization of iron for clearance from the cell via the cytosol. This model may be useful in characterizing the determinants of effective chelation in patients.