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C V Tondo

Publications and source records attributed to C V Tondo.

17 recordsLinked to original sources
PubMed1987

Osmometric study of the subunit dissociation of hemoglobin Porto Alegre [beta 9(A6)Ser----Cys] dissulfide polymer.

The hemoglobin Porto Alegre (HbPA) disulfide polymer dodecamer and the HbPA, HbA disulfide polymer octamer subunit dissociation by NaCl was studied by measuring the osmotic pressure of CO-hemoglobin solutions at pH = 6.9 and 20 degrees C. The dissociation equilibrium constants were evaluated from the osmotic pressure data. The subunit dissociation of the two types of disulfide polymers follows a reaction of the type A3 in equilibrium 3A. The HbPA disulfide polymer dodecamer appears to be more susceptible to NaCl induced dissociation than is normal HbA and less resistant to dissociation on protein dilution. The HbPA, HbA disulfide polymer octamer appears to be much more susceptible to dissociation on protein dilution than is the HbPA disulfide polymer dodecamer and normal HbA. The standard free energy of dissociation of the HbPA disulfide polymer at 2 M NaCl is delta GOD(25 degrees C) = 12 kcal/mole. The type of dissociation reaction (A3 in equilibrium with 3A) support the conclusion that the HbPA disulfide polymer has a quaternary molecular structure of a closed ring of three tetramers.

Hemoglobin A↗
PubMed1985

Kinetic study of hemoglobin Porto Alegre [beta 9(A6)Ser----Cys] disulfide polymer reduction.

The cleavage of HbPA disulfide polymer by GSH and its indirect cleavage by yeast glutathione reductase, via reduced glutathione is obtained. Decreasing the initial proportion of GSH in the hemolysate increases the formation of HbPA disulfide polymer. In the experimental conditions used, yeast glutathione reductase is unable to perform the direct cleavage of the mixed disulfide of HbPA and GSH, using it as substrate. The reduction of HbPA polymer to tetramers by DTE is analyzed by a pseudo-first-order kinetic and two rate constants are obtained. That of 265 X 10(-3) min-1 should be concerned with one disulfide of the closed ring and one of the open ring structure of dodecamer, while that of 38 X 10(-3) min-1 is related to disulfide reduction of the octamer. The enthalpy of activation values of 8.0 kcal.mol-1 an 17.4 kcal.mol-1 obtained, from the Arrhenius plot, for the "fast" and "slow" rate disulfide reduction, respectively, are indicative that a strong conformational strain of S--S bonds in the closed ring structure is maintained. The entropy of activation values of 24 e.u. and 52 e.u. are found for the activation of disulfides from dodecamers and octamers, respectively.

Brazil↗
PubMed1982

A biophysical model of lysozyme self-association.

The concentration dependence of the self-association of hen egg-white lysozyme was studied spectrophotometrically at pH 6, 25 degrees C, and low ionic strength within a concentration range of 2.5-50 micrograms/ml. Of several possible mathematical models, an ideal or nearly ideal two-stage model representing an equilibrium between monomers and dimers and between dimers and trimers best describes the data. The dimerization and trimerization constants were found to be 2.5 x 10(-2) and 38 x 10(-2). Dialysis experiments confirmed that the mechanism involves three associating species. A "head-to-tail" contact between the associating sites was inferred from dialysis studies of the effect of indole and imidazole derivatives on lysozyme self-association.

Animals↗
PubMed1982

Hemoglobin types in Brazilian populations.

Population surveys performed in different Brazilian ethnic groups, and comprising 23,606 subjects, disclosed, besides the common S and D types, hemoglobins G and Por to Alegre, as well as high F, A'2 and an apparently unstable A2 variant. Additional studies on isolated families revealed the occurrence of hemoglobins I, Niterói, D Punjab, M Boston and J Rovigo. Screening for sickle cells was also performed on 17,412 individuals. Detailed clinical studies on series of sickle cell anemics were also performed. Due to their special interest, the physico-chemical properties of Hb porto Alegre are reviewed in some detail.

Black People↗
PubMedDate not supplied

Asymetric tetramer in a second occurrence of hemoglobin Porto Alegre alpha A2betaAbeta9Ser replaced by Cys.

Hemoglobin Porto Alegre is an abnormal human hemoglobin which polymerizes by formation of intermolecular disulfide bonds between the mutant cysteinyl residues at the beta9 position. Biochemical studies of this abnormal hemoglobin from a heterozygous carrier of a second family of carriers indicates that an asymmetric tetramer alphaA2betaAbeta9 Ser replaces Cys is formed after polymerization. Functional studies of the polymer indicate that its oxygen binding properties are unaffected by the polymerization and that its oxygen affinity is somewhat higher than that of normal hemoglobin; it has a slightly reduced heme-heme interaction and a normal Bohr effect.

Cystine↗