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Biomedical subjects

I Aviram

Publications and source records attributed to I Aviram.

At least 55 records · Page 3Linked to original sources
PubMed1978

The reaction of ferrous leghemoglobin with hydrogen peroxide to form leghemoglobin(IV).

Ferrous leghemoglobin reacts with hydrogen peroxide to form the stable product, leghemoglobin(IV). The reaction follows second order kinetics (k = 2.24 X 10(4) M-1 S-1 at 20 degrees C) and may be regarded as a single-step, two-electron oxidation. Ferric leghemoglobin is not an intermediate. The oxidation state of leghemoglobin(IV) is established by reductive titration with dithionite; 2 eq of dithionite are required to convert 1 mol of leghemoglobin(IV) to ferrous leghemoglobin. An outstanding property of leghemoglobin(IV) is its stability, little change is noted after 12 h at 25 degrees C. Leghemoglobin(IV) differs from the higher oxidation states of other hemoglobins and myoglobins in that it does not react with hydrogen peroxide to form the oxygenated protein.

Dithionite↗
PubMed1976

A spectrophotometric and fluorimetric study of alkaline transitions of Euglena cytochrome c 552.

The behavior of the photosynthetic cytochrome c552 upon titration with alkali depends on the ionic composition of the medium. In water the disappearance of the 695-nm band, indicating the displacement of the methionine ligand, as well as a remarkable tryptophan fluorescense enhancement, follow a single proton titration curve with pK of 10.0 and n=1.0. The product is a low spin type protein. In salt-containing media two successive steps are observed: in the first one, completed at about pH 10.3, a high-spin form of cytochrome c 552 is obtained and relatively small fluorescence enhancement is detected. In the second step, more profound fluorometric changes occur, while the material reverts to its low-spin form. Addition of salts to an alkaline solution of cytochrome c 552 in water results in the formation of a 600-nm high-spin band with a concomitant quenching of tryptophan fluorescence. The results imply that at high pH unfolding of the molecule is evident only when the low-spin product is obtained. In the high-spin alkaline form, the methionine ligand is probably displaced from iron coordination by hydroxyl ions, while in the low-spin alkaline form methionine may be replaced by a lysyl residue of the cytochrome c 552 protein. The results imply that the lysyl residue is available for coordination in salt solutions at a higher pH than in water.

Cytochrome c Group↗
PubMed1975

Physicochemical properties of two atypical cytochromes c, Crithidia cytochrome c-557 and Euglena cytochrome c-558.

Cytochrome c-557 from Crithidia oncopelti and cytochrome c-558 from Euglena gracilis are mitochondrial cytochromes c that have an atypical haem-binding site. It was of interest to know whether the loss of one thioether bond affected the physicochemical properties of these cytochromes. The thermodynamic parameters of the redox potential were measured. The reaction with imidazole, the kinetics and thermodynamics of the alkaline isomerization and the effect of heating on the visible spectrum are described for the ferricytochromes. The kinetics of the loss of cyanide, the spectral changes occurring on reduction with dithionite at alkaline pH values and the reactivity with CO are described for the ferrocytochromes. In many respects the cytochromes of the two protozoans are very similar to the cytochromes of horse and yeast. The ferricytochromes do, however, undergo a reversible transition to high-spin species on heating, which may be due to the more flexible attachment of the prosthetic group. Similarly the alkaline isomers of cytochromes c-557 and c-558 give rise to high-spin proteins above pH 11. The alkaline isomerization of cytochrome c-558, involves a pKobs. of 10 and kinetics which do not obey the model of Davis et al. [(1974) J. Biol. Chem. 249, 2624-2632] for horse cytochrome c. It is proposed that a model involving two ionizations, followed by a conformation change, may fit the data. Both cytochromes c-557 and c-558 combine slowly with CO at neutral pH values.

Animals↗