Horse heart ferricytochrome c: conformation and heme configuration of high ionic strength acidic forms.

The absorption, circular dichroism, and resonance Raman spectra of horse heart ferricytochrome c in the presence of 0.2 M KCl, 0.1 M NaClO4, and 0.2 M KNO3, in the pH region 7 to 0.5, have been investigated to determine the nature and the course of the processes involved. As in the absence of salts (Myer, Y., and Saturno, A. F. (1990) J. Protein Chem, 9, 379-387), the change from neutral to low acidic pH's in the presence of salts is a three-step process: state IIIs----state IIIS,a----state IIS----state IS, with pKa's of 3.5 +/- 0.2, 2.2 +/- 0.2, and 1.1 +/- 0.2, and with two, one, and one number of protons, respectively. The addition of salts at neutral pH's has little or no effect on the protein conformation and the heme-iron configuration (i.e., they remain the same, low-spin hexacoordinated heme iron with a Met-80-Fe-His-18 axial coordination), but such addition does cause a slight tightening of the heme crevice and the enlargement of the porphyrin core. State IIIS,a is a folded state with about the same degree of folding and with a similar spin state and coordination configuration of iron, but the heme crevice is loosened and the porphyrin core is smaller. Both states IIS and IS are also essentially folded forms, but with a smaller degree of protein secondary structure. State IIS has a high-spin hexacoordinated heme iron with a water molecular and a protonated and/or hydrogen-bonded imidazole of his-18 as the two axial ligates; and state IS has a high-spin pentacoordinated heme iron, which is about 0.49 A out of the porphyrin plane, with a protonated and/or hydrogen-bonded imidazole nitrogen as the only axial ligate. The addition of anions causes the stabilization of the protein secondary structures and the state IIIa----state II transition. The mode of effectiveness of anions appears to be nonspecific (i.e., because of electrostatic shielding and/or disruption of salt bridges).

Horse heart ferricytochrome c: conformation and heme configuration of low ionic strength acidic forms.

Resonance Raman, absorption and circular dichroism spectroscopic studies of the stable forms of horse heart ferricytochrome c in the pH range 6-0.8 and at the lowest possible ionic strengths, in water, and at 30 degrees C are reported. The neutral pH form, state III, changes to the acidic pH form, state I, through a three-step process: state III in equilibrium with IIIa in equilibrium with state II in equilibrium with state I, with pKa's of 3.6 +/- 0.3, 2.7 +/- 0.2, and 1.2 +/- 0.2, depending on the monitoring probe, respectively. State IIIa ferricytochrome c is like state III (i.e., with the Met-80-sulfur-iron linkage and a closed heme crevice) but with a higher degree of folding and a slightly larger porphyrin core. State II ferricytochrome c is an unfolded form with an open heme crevice and no Met-80-sulfur-iron linkage. The heme iron is high-spin, and hexacoordinated with weak ligand-field groups, water, and nitrogen of the protonated/hydrogen-bonded imidazole of the His-18 residue at the axial positions. The state I form also lacks the Met-80-sulfur-iron linkage and has an open heme crevice like the state II form; however, it is less unfolded and has a high-spin pentacoordinated heme iron, with the nitrogen of the imidazole of His-18 as the axial ligate, which is out of the porphyrin plane by about 0.45 A.

Tensión arterial en escolares de un medio rural / Blood pressure in school children of a rural environment

La TA en pacientes pediátricos no ha sido estudiada adecuadamente en Venezuela. El presente trabajo se realizó para determinar las cifras tensionales según edad y sexo en escolares de las poblaciones rurales de El Cortijo y Los Bagres, Dtto. Sanitario No. 3, Ed. Aragua y correlacionario con peso, talla, y antecedentes familiares. La muestra fue de 184 niños (94 varones y 90 hembras), con edades entre 7 y 14 años. Se registró el primer, cuarto y quinto ruido de Korotkoff en posición acostado, sentado y de pie, con esfigmomanómetro de mercurio. No se observó diferencia significativa entre las medias aritméticas de varones y hembras. Se evidenció una correlación significativa (p<0,05) y positiva entre TA y peso en la mayoría de los casos. Las cifras de TA registrada en posición sentado fueron siempre las más bajas en ambos sexos (p<0,05). La prevalencia de lecturas elevadas en la primera medición fue de 13,6% (6,0% en varones y 7,6% en hembras, p>0,05); el 5,6% mantendrán cifras elevadas a las cuatro semanas

Kinetics of unfolding and folding of horse heart ferricytochrome c with urea.

Kinetic data for the reversible folding and unfolding by urea of horse heart ferricytochrome c, in 0.05 M phosphate + 0.25 M Na2SO4 buffer, pH 7.0, in the region of the main denaturation transition, 4-9 M, are reported. Stopped flow technique and absorptivity at 695, 528, and 361 nm as the monitoring probes were used. The decay profiles in the region of the transition 6-7.2 M urea are adequately described by a rate law with two exponential decay terms, but a rate law with only a single term is found to be applicable at the lower and higher limits of the transition. The apparent rate constant for the fast phase exhibits urea dependence with a minimum value at about 6.5 M urea, while the apparent rate constant of the slow phase is found to be independent of urea and has a value of 0.04 +/- 0.02 s-1. The assignment of the two apparent rate constants to the respective steps and the characterization of the processes involved were carried out through correlation of the kinetic data to the results from equilibrium studies for urea denaturation ( Myer, Y. P., MacDonald, L. H., Verma, B. C., and Pande, A. (1980) Biochemistry 19, 199-207). A mechanism X1 in equilibrium X2 in equilibrium D, where the first step is the urea-dependent unfolding and folding, and the second, an apparent urea-independent process involving possibly reorganization of the unfolded form X2, has been proposed to account for the above findings. The X2 in equilibrium D process is further considered in light of various possibilities: the incorrect folding of the unfolded form, the alteration of heme iron coordination, and the cis-trans isomerization of proline.