Bioinorganic chemistry最新文献

Variations of the copper distributions subsequent to copper imput changes have been studied in normal male Wistar rats. A fasting period (48 or 96 hr) produces significant variations only in the kidneys. d-Penicillamine administered during the fasting period induces a significant decrease of the copper content also in the liver. When injected subcutaneously. CuCl₂ (1–2 mg/kg body weight) stores up first in the liver and second in the kidneys (24 hr after a 2-mg/kg body-weight injection, 80% of the copper is found in the liver and 6% in the kidneys). d-Penicillamine administered subcutaneously to animals treated with CuCl₂ brings the exceeding copper of the liver to normal values within 6 hr. A prominent role of the liver and the kidneys in the copper metabolism is discussed.

The nickel(II) derivative of carbonic anhydrase and its adducts with inhibitors have been investigated through electronic and nuclear magnetic resonance (nmr) spectroscopy. The metal ion in the pure enzyme is six-coordinated, and there is evidence for at least one water molecule in the coordination sphere. Inhibitors replace the water molecule, still giving rise to six-coordinated adducts. The affinity of the inhibitors is decreased at alkaline pH but cannot be related to a single ionization in the active site cavity.

Cu(II)-Poly-(l-ornithine) complexes in aqueous solution have been studied using potentiometric titration and absorption and circular dichroism spectra. As in the case of Cu(II)-poly(L-arginine) complexes studied previously, two types of compounds have been detected, labeled complexes I and II. Complex I contains two amine nitrogens and two water molecules coordinated to the copper. Complex II, two amine and two amide nitrogens. Amide nitrogen coordination confers optical activity to the copper d-d transitions. Furthermore, amine and amide nitrogen coordination to the copper are characterized by charge transfer transitions at 250 and 320 nm respectively which were already identified in Cu(II)-poly(L-arginine) systems.

For studies of interactions between Co²⁺ and adenosine 5′-diphosphate or adenosine 5′-triphosphate (ADPH₄⁺ and ATPH₅⁺ in strongly acidic medium) visible circular dichroism (d-d transitions of Co²⁺) and ultraviolet circular dichroism (adenine transitions) have proven to be very sensitive to structural changes. Drastic variation of spectra as a function of pH and concentration enabled us to show the existence of various species, to state their stoichiometry and eventually, their self-association. With ATPH₂^2-, C.D. results are in agreement with recent N.M.R. results. With ligands bearing three negative charges, complexes (1 metal:2 nucleotides)_n are formed in which bases of the two nucleotides of the molecule are self-associated. With ADP^3-, the visible C.D. spectrum of this complex is intense and hides the spectra of the complexes formed with other protonated species of ADP; this self-associated complex is detected up to a lower limit of 5 × 10^-4 M concentration. With ATPH^3-, a complex exhibiting the same characteristics as the one with ADP^3- is formed but in about twenty times less amount which explains why it was not detected by potentiometry. With 0.1 M ATP^4-, dimeric (or polymeric) complexes, of 1:2 and 1:1 stoichiometry are observed. With 0.01 M ATP^4-, 1:1 monomeric and 2:1 dimeric (or polymeric) complexes are detected. The interactions between Mn²⁺ ions and ADP or ATP have been studied by C.D. on the UV range. The same species as with CO²⁺ ions have been found but the 1:2 complex formation with ADP^3- was shown to occur to a lesser exten and was not observed below a 10^-2 M ADP concentration.

Three 6 week-old lambs were injected with carrier-free selenium-75 as sodium selenite initially and again after 6 days. One lamb received no further injections whereas the other two received injections of either vitamin E or unlabeled Na₂SeO₃ when the first selenium-75 injection was given. Selected tissues were removed at autopsy 10 days after the first injection. The cytosol from homogenates of these tissues was subjected to gel chromatography, and the elution profiles determined for radioactivity, protein content, and glutathione peroxidase activity using either hydrogen peroxide or cumene hydroperoxide as substrates. The selenium-75 was found to be distributed mainly between 2 different MW peaks. The larger MW seleno-peak (90,000) possessed both glutathione:hydrogen peroxide oxidoreductase, and glutathione:cumene hydroperoxide oxidoreductase activities, but the smaller MW seleno-peak (about 10,000) possessed no glutathione peroxidase activity. A peak of about 60,000 daltons containing only glutathione:cumene hydroperoxide oxido-reductase activity and no selenium-75 was found primarily in the liver and kidney. Vitamin E had no effect on the elution profiles. Selenium status of the animal had only a minor effect on the selenium-75 distribution in the cytosol, but had a marked effect on the absolute amount of label taken up by tissues.

The dietary selenium intakes of a young couple residing in Southern California were determined to be 107 and 99 μgrams/day for the husband and the wife, respectively, on the basis of a 30 day study. For other young adult Californians, the selenium intakes were estimated from 90 to 168 μgrams/day. The highest intakes were observed in individuals subsisting on diets rich in whole wheat grain cereal products and seafoods. The selenium concentrations in whole blood of the subjects under study correlated with the dietary selenium intakes directly (P<0.001). The administration of 150 μgrams of selenium/day in the form of commercially available supplements increases the blood selenium concentrations. After 3 weeks of supplementation, the selenium concentrations in whole blood of our subjects reached 0.21 μgrams/ml. Prolonged supplementation at higher Se dosage levels causes further increases of the blood concentrations: Two individuals who had been ingesting 350 and 600 μgrams/day for 18 months exhibited blood selenium levels of 0.35 and 0.62 μgrams/ml. The blood selenium concentration of all subjects declined slowly after cessation of supplementation. Selenium uptake from the supplements was not affected by the joint administration of zinc supplements at 15 mg zinc/day. Glutathione peroxidase blood levels did not correlate with blood Se concentrations.

The inhibition of several dehydrogenase enzymes by cis- and trans- Pt(NH₃)₂Cl₂ have been measured in the presence of baker yeast ribonucleic acid (RNA), calf thymus and salmon sperm deoxyribonuclic acid (DNA) and several mononucleotides (AMP and ATP). The binding constants for the interaction of the platinum complexes to the nucleotides have been calculated and a comparison of those values to the previously calculated platinum complex-enzyme binding constants strongly suggest that platinum compounds are more tightly bound to the enzymes. The binding of the platinum complexes to most of the enzymes was decreased in the presence of any nucleotide, yet it was observed that when using rabbit muscle (M₄) lactate dehydrogenase the mononucleotides reduced the binding to a lesser degree while the polynucleotides actually enhanced the platinum-enzyme interaction. The implications of these interactions are discussed.

The interactions of angiotensin II and a synthetic analogue, [Asn¹, Val⁵] angiotensin II, with Ca²⁺ and Tb³⁺ have been monitored using the intrinsic fluorescence of the tyrosine residue at position 4 in both molecules. The data indicate that angiotensin II binds both metals with a dissociation constant of ∼1 × 10⁻⁴ M⁻¹, while no significant binding was observed with the amide analogue. This suggests that the side chain carboxyl group of aspartic acid forms part of the binding site. Since the value of the dissociation constant suggests chelation of the metals by the hormone, the terminal carboxyl group of the peptide is also probably involved in metal binding. The fact that energy transfer was observed between Tb³⁺ and the tyrosine of angiotensin places the hydroxl or carbonyl group of the tyrosine close to the metal binding site.

Solutions of Busycon canaliculatum have been studied by light scattering. In 0.05 M Trizma buffer + 0.1 M NaCl at pH 7.0 at 14°, the weight-average molecular weight is 8.9 X 10⁶. In the presence of added CaCl₂ (0.02 M), the molecular weight of the protein increases to 10.7 X 10⁶, and the second virial coefficient is reduced. At pH 9.95, the molecular weights with and without 0.02 M CaCl₂, are 3.7 X 10⁶ and 1.3 X 10⁶, respectively; and the effect of Ca⁺⁺ in reducing the second virial coefficient is much greater than at pH 7.0. These results can be understood on the basis that at pH 7.0, Ca⁺⁺ increases the association of hemocyanin, by binding and intermolecular linkage through the carboxyl groups of protein side chains. At pH 9.95, amino groups are deprotonated and therefore also become available for Ca⁺⁺ binding. The relative effect of Ca⁺⁺ in enhancing the association of hemocyanin therefore becomes greater at the higher pH.