1,721,063 research outputs found
Hemocyanins: molecular architecture, structure and reactivity of the binuclear copper active site.
No full textConformational Differences between Human Holo- and Apo-Ceruloplasmin Studied by Small Angle X-Ray Scattering
No full text
EFFECTS OF ANIONS CA-2+, MG-2+, AND ALIPHATIC-ALCOHOLS ON THE REACTION OF HEMOCYANIN WITH CYANIDE
No full textDissociation kinetics of hemocyanin from Octopus vulgaris
No full textThe native form of hemocyanin (Hc) from Octopus vulgaris can be completely dissociated, at alkaline pH and in the presence of EDTA, from 49S decamers to 11S monomers. The kinetics of this process was studied, using a Bio-Logic stopped flow system, by following the time dependence of the 450-nm light intensity, scattered at 90 degrees, in the 7.9-8.8 pH range. All experimental traces were best fitted by a sum of three exponential decay functions. We then tried to best fit these decay functions with a series of kinetic models, the best of them resulting in one whose dissociation of decamers to monomers takes place in three consecutive and irreversible steps, with a highly cooperative step concerning dissociation of octamers to dimers, which appears to be the only intermediate species. This model was preferred over several others, not only for the best norm value but also for the best accordance between each calculated and experimental kinetic parameter (rate constants and amplitudes). Although other more complex models may be considered, our best fit model represents the simplest one, which is able to describe the observed dissociation kinetics
Comparative structural analysis of low-molecular mass fragments of Rapana venosa hemocyanin obtained using two different procedures
No full textDifferent fragments of the hemocyanin (Hc) isolated from the gastropod Rapana venosa containing a single functional unit (50 kDa), two functional units (100 kDa) and three functional units (150 kDa) were obtained in a dissociating buffer in the presence of Zn2+ and purified to homogeneity. Their conformations in solution were studied by means of small angle X-ray scattering (SAXS) and compared with those of the corresponding fragments previously obtained by limited proteolysis [Arch. Biochem. Biophys., 2000, 373, 154]. The overall shape of each fragment was determined using an ab initio approach. The crystal structures of the functional unit e from the same Hc and from another molluscan Hc (Octopus dofleini) were used to model 100 and 150 kDa fragments using rigid body movements to fit the corresponding SAXS patterns. Interesting differences were observed between the functional unit organization in the low-molecular mass fragments according to the two preparation methods, suggesting different localizations within the 11S functional subunit.[...
Emission Quenching Mechanisms in Octopus vulgaris Hemocyanin: Steady-State and Time-Resolved Fluorescence Studies
No full textFluorescence emission properties of various derivatives of Octopus vulgaris hemocyanin, namely, oxy, deoxy, met, half-met, half-apo, and apo derivatives, are studied by means of time-resolved and quenching techniques. Fluorescence decay can be satisfactorily fitted by two-exponential analysis in all hemocyanin derivatives. Fluorescence quenching experiments, using acrylamide, iodide, and a combination of the two, are carried out in order to correlate the observed lifetimes with different classes of fluorophores, distinguishable by their accessibility to the external quenchers. Fluorescence lifetimes of 1.2, 2.1, and 5.5 ns are attributed to buried, partially exposed, and fully exposed tryptophans, respectively, in 11S hemocyanin at pH 8.5. For 50S hemocyanin, the lifetime pattern is very similar, but a shortening of all lifetime values is observed. The fluorescence of the class of partially exposed tryptophans, situated in close proximity to the active site, is totally quenched in oxy-..
The binding of Cd(II) to the hemocyanin of the Mediterranean Crab Carcinus maenas
No full textThe interaction of Carcinus hemocyanin with Cd(II) was studied. The incubation of the apoprotein with the metal yields a derivative containing 1 g-at. of EDTA-stable Cd(II) per 75 kDa. Spectroscopic data ruled out Cd(II) coordination to tryptophan or cysteine residues. The optical activity and fluorescence properties of the protein are affected by Cd(II) binding and indicate a rearrangement of tryptophan residues. The poor Cd(II) binding to the oxy-form and the resistance of Cd(II)-hemocyanin to EDTA treatment and to the regeneration by Cu(I) strongly indicate that Cd(II) binding to apohemocyanin occurs at the copper-free active site. During the metal-binding process, a marked increase of light scattering is observed. This effect, however, is reversible provided that the incubation medium contains SCN- and glycine as exogenous ligands of the metal in the bulk solution
- …
