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Biomedical subjects

C E Castro

Publications and source records attributed to C E Castro.

At least 37 records · Page 2Linked to original sources
PubMed1978

Oxidation of heme proteins by alkyl halides: a probe for axial inner sphere redox capacity in solution and in whole cells.

Iron(II) porphyrins in homogeneous solution, in heme proteins, and in intact human erythrocytes and lysed cells are oxidized by certain alkyl halides to the corresponding iron(III) complexes at room temperature. The mechanism established for the oxidation of hemes in homogeneous solution operates at all levels of biological integrity. It is an axial inner sphere process. Deoxyhemoglobin has about the same reactivity within and without cells. The speed of the reaction with the proteins is primarily governed by the steric accessibility to iron. The reactivity of an array of iron(II) proteins accords well with theoretical prediction. In contrast the reactivity of cytochrome b5 does not. An examination of the oxidation and reduction of this protein was additional mechanistically defined reagents (trinitrobenzene and hydroquinone) shows it to be in the G rather than C conformation. The unusual redox characteristics of this protein can be rationalized on this basis.

Animals↗
PubMed1978

Oxidation of low-spin iron(II) porphyrins by molecular oxygen. An outer sphere mechanism.

Hexacoordinate low-spin iron(II) porphyrins are oxidized by molecular oxygen in amine solvents at room temperature by a process that is acid dependent. The visible and NMR spectra of solutions of the iron complexes and the influence of axial ligands upon the rate of oxidation are consistent with an outer sphere mechanism that entails the dissociation of a protonated 1:1 iron porphyrin-oxygen pi complex as the rate-limiting step.

Chemical Phenomena↗
PubMed1978

Conversion of oxyhemoglobin to methemoglobin by organic and inorganic reductants.

Human oxyhemoglobin is converted to methemoglobin by a wide array of organic and inorganic reductants. Depending upon the concentration and nature of the reductant, varying amounts of deoxyhemoglobin are produced. The general overall sequence is: FeO2 leads to (1) FeIII leads to (2) FeII. The intermediacy of methemoglobin can be demonstrated by direct spectral observation and by cyanide trapping. For organic reductants, the second-order rate constants for (1) vary from greater than 300 (phenylhydroxylamine) to 1.4 X 10(-4) M-1 s-1 (malononitrile). Generally the rates parallel the ease of hydrogen abstraction by iron-bound oxygen from the substrate, and simply hydrocarbons are reactive. Rates for these processes have been ascertained with recrystallized protein, lysed cells, and intact human erythrocytes. At room temperature oxyhemoglobin quantitatively converts benzaldehyde to benzoic acid and hydroquinone to benzoquinone. Rates for inorganic species (process 1) range from greater than 7 X 10(3) (chromous ion) to 0.015 M-1 s-1 (ferrocyanide). Ferrous ion rapidly deoxygenates oxyhemoglobin by direct attack on the oxy complex but methemoglobin is not an intermediate with this reagent. Taken together the results support the theoretical prediction that reductants should oxidize oxyhemoglobin, and they demonstrate at least some degree of radical character to the oxy complex.

Anions↗
PubMed1977

Biodehalogenation.

Haloorganic biocides are widely employed as soil fumigants to combat the destructive action of plant parasitic nematodes and fungi. These substances are dehalogenated by soil organisms, principally species of Pseudomonas and Flavobacteria, to nontoxic metabolities. The paths of metabolism of a vareity of simply alkyl halides are described with emphasis upon the biodehalogenation step.

1-Propanol↗
PubMed1975

Conformational isomerism and effective redox geometry in the oxidation of heme proteins by alkyl halides, cytochrome c, and cytochrome oxidase.

In contrast to its lethargy at physiological pH, horse heart cytochrome c can be oxidized at room temperature by the axial inner sphere oxidant bromomalononitrile (BMN) at higher acidities. The following stoichiometry obtains: 2Fe11 c + BrCH(CN2) + H+ leads to 2FeIII c + CH2(CN)2 + Br-, and the rate law is given by: rate = k2(FeIIc)(BMN). At an ionic strength of 1.0 (KCl), second-order rate constants vary from 300 l. per mol per sec (pH 2-3) to 0(pH 9). Below pH 6 there is a noticeable increase in rate with ionic strength while there is no specific salt effect for the process. At pH 7.4 there is no influence of added salt (0.01-1.0 M) upon the slow rate of reaction. The vast changes in rate occur over a pH region (3-6) in which only very minor changes in the visible spectrum of the cytochrome are manifest. The results are interpreted in terms of a conformational isomerism of cytochrome c in which the effective redox geometry alters from a predominantly "short C" form (in which an axial position is available for substitution) at lower pH's to a predominantly "C" form (axial positions encumbered) in the physiological region. At 5 degrees, pH 7.4, both hemes of beef heart cytochrome oxidase are oxidized by the addition of BMN (k2 = 29 plus or minus 3 l. per mol per sec). However, the reaction is inhibited by potassium cyanide and the protein containing iron(II) cyt alpha along with the cyano adduct of iron(II) or iron(III) cyt alpha3 is inert. The results demonstrate cytochrome alpha3 as the site of reaction and that alpha reduces alpha3 in the process. Cytochrome oxidase does catalyze the oxidation of cytochrome c with BMN as substrate. Taken together the results provide additional support for a recent theory and they demonstrate BMN to be an efficient probe for the effective redox geometry of a hemoprotein in solution.

Animals↗