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Biomedical subjects

L Zolla

Publications and source records attributed to L Zolla.

33 records · Page 2Linked to original sources
PubMed1982

Spectroscopy of (carbon monoxy)hemocyanins. Phosphorescence of the binuclear carbonylated copper centers.

The luminescence of CO-hemocyanin has been studied in several hemocyanins from both arthropods and molluscs. All of them show an emission in the region 550-560 nm with quantum yield = 0.2-0.4, though individual differences are apparent. Solvent composition (as well as the presence of calcium and lanthanides) has no effect on the emission. Lifetimes of this luminescence are in the range 60-140 microseconds, indicating that the emitting state may be a triplet. The presence of both copper atoms (Cu+) per CO binding site is required for the luminescent state since half-met and half-apo derivatives do not show such an emission. Though not clearly related to any of the functional properties, systematic differences in luminescence parameters are apparent between arthropodal and molluscan hemocyanins. Limulus hemocyanin appears to be very different from both types of hemocyanin.

Animals↗
PubMed1982

Ligand binding and stereochemical effects in hemocyanins.

The Bohr effect in the binding of O(2) and CO to Helix pomatia beta-hemocyanin has been estimated by the potentiometric titration method. On the basis of the results, as well as other information available, we conclude that binding of O(2) to hemocyanin is associated with a quaternary allosteric transition (T-->R), while binding of CO is not. This conclusion is in agreement with previous results, which indicate that homotropic interactions are observed only for the binding of O(2) to the active site of hemocyanins. This is in marked contrast to the behaviour of hemoglobins which, otherwise, share with hemocyanins a number of important features, in spite of basic chemical differences. The stereochemical requirements of O(2), which forms a bridge between the two copper atoms in a site, have to be considered essential for the onset of cooperativity in hemocyanins.

Journal Article↗
PubMed1981

Binding of organic ions by proteins. 2. Effects of 1-benzyl-3-indazoleoxyacetate at low concentration on the oxygen affinity of human hemoglobin.

The oxygen equilibrium of human hemoglobin has been studied in the presence of 1-benzyl-3-indazoleoxyacetate (BZ). The results show that: (a) The overall oxygen affinity of hemoglobin is a function of BZ concentration, but the cooperative character of the equilibrium curve appears insensitive to the drug up to the maximal concentration studied (5 x 10(-2) M); (b) The functional expression of the interaction between hemoglobin and BZ is not affected by the presence of protons, i.e., the change in oxygen affinity determined by BZ is the same at any pH value studied; (c) The aromatic region of BZ molecules is of primary importance for the functional change of hemoglobin; (d) The difference in moles of BZ bound per mole of tetrameric unliganded and oxygenated hemoglobin corresponds to 2; these functionally relevant binding sites on the protein are probably located at alpha 1, beta 1 and alpha 2 beta 2 interfaces; (e) Thermodynamically, entropy effects dominate the reaction between hemoglobin and BZ.

Dose-Response Relationship, Drug↗
PubMed1980

Root effect of Panulirus interruptus hemocyanin.

Panulirus interruptus hemocyanin exhibits a progressive decrease in oxygen affinity and a parallel loss of cooperativity with decrease in pH, resulting in an apparent loss of the oxygen-binding capacity of the protein. For a characterization of this system, oxygen-binding curves have been determined over the complete range of oxygen saturation, applying a special technique which involves high-pressure spectrophotometry. Although the oxygen-binding behavior as a function of pH is complex and cannot be described within the frame of a simple two-state Monod-Wyman-Changeux model, the observed Root effect is clearly related to a progressive stabilization of a low oxygen affinity state of the protein and functional heterogeneity is not apparent.

Animals↗
PubMed1977

The effect of macromolecular polyanions on the functional properties of human hemoglobin.

The binding of dextran sulphate and heparin to human hemoglobin and their effect on the properties of gas transport have been investigated. Both dextran sulphate and heparin are strongly bound by oxy-hemoglobin as well as deoxyhemoglobin and the stoichiometry of the binding (polyanion/tetrameric hemoglobin) is less than unity; sedimentation analysis gives indication for the existence of octomers. The oxygen affinity of hemoglobin is decreased, to the same extent, by both dextran sulphate and heparin. This effect is pH-dependent. In addition the polyanions affect the position and the magnitude of the Bohr effect. In the presence of dextran sulphate the recombination of hemoglobin with carbon monoxide after flash photolysis is biphasic and the fraction of quickly reacting material increases with dilution of the protein.

Dextrans↗
PubMedDate not supplied

Metal binding to Pseudomonas aeruginosa azurin: a kinetic investigation.

The interaction between azurin from Pseudomonas aeruginosa and Ag(I), Cu(II), Hg(II), was investigated as a function of protein state, i.e. apo-, reduced and oxidised azurin. Two different metal binding sites, characterized by two different spectroscopic absorbancies, were detected: one is accessible to Ag(I) and Cu(II) but not to Hg(II); the other one binds Ag(I) and Hg(II) but not copper. When added in stoichiometric amount, Ag(I) shows high affinity for the redox center of apo-azurin, to which it probably binds by the -SH group of Cys112; it can displace Cu(I) from reducedazurin, while it does not bind to the redox center of oxidizedazurin. Kinetic experiments show that Ag(I) binding to the reduced form is four times faster than binding to the apo-form. This result suggests that metal binding requires a conformational rearrangement of the active site of the azurin. Interaction of Ag(I) or Hg(II) ions to the second metal binding site, induces typical changes of UV spectrum and quenching of fluorescence emission.

Azurin↗