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K H Mayo

Publications and source records attributed to K H Mayo.

96 records · Page 6Linked to original sources
PubMed1980

Carp hemoglobin. I. Precise oxygen equilibrium and analysis according to the models of Adair and of Monod, Wyman, and Changeux.

Precise oxygen equilibria for carp hemoglobin had been measured from about 1% to 99% saturation at 15 degrees C. The determinations were made in 2,2-bis(hydroxymethyl)-2,2',2"-nitrilotriethanol buffer and in phosphate buffer in the presence and absence of P6-inositol (IHP). At the highest cooperativity, carp hemoglobin has a maximum Hill coefficient, n, of 2.3 and free energy of interaction, delta GI, of 2100 cal/site; addition of IHP decreases these values to 1.6 and 1640 cal/site, respectively. NaCl at 0.1 M or 0.2 M increases both delta GI and n. Intrinsic association constants, ki, were estimated by nonlinear least square fit of Hill plots; their values are more sensitive to pH than normal adult human hemoglobin (HbA). Identical values of nmax and ki were obtained with either one of the two major components of carp hemoglobin as with the hemolysate under the same conditions. IHP, whose effect on carp hemoglobin is much smaller than that on HbA, alters all ki values rather indiscriminately. Since IHP affects k4, it binds to Hb(O2)3 as well as the lower oxygenated species. The same is true for inorganic phosphate at pH < 8.3; however, above this pH, the phosphate ion is apparently expelled when the third heme is oxygenated since addition of PO(3-)4 does not change k4. From the intrinsic association constants, one concludes that carp hemoglobin in the cooperative regime undergoes allosteric transition after oxygenation of the third heme. Lowering of cooperativity by pH changes seems to shift conformational transitions to earlier stages of oxygenation. Parameters of the Monod, Wyman, and Changeux model were estimated by a similar nonlinear least square procedure. In the phosphate system, values of KR, c, and L are found to be 8.2 mm Hg-1, 1.3 x 10(-2), and 4.2 x 10(6) at pH 7.20. Changes of pH in either direction increases the values of KR and L and decreases the c value negating assumptions for pH-independent T and R quaternary structures.

Animals↗
PubMed1980

Carp hemoglobin. II. The alkaline Bohr effect.

The Bohr effect of carp hemoglobin has been determined by differential titration, by direct acid-base titration, and by calculation from precise oxygen equilibrium data over a wide pH variation. The results for the hemolysate and the two major components are essentially identical. At pH 6.9 in the vicinity of maximum cooperativity and maximum Bohr effect, the protein releases 3.7 protons in the absence of added ions. This Bohr curve above pH 7 is not changed by the presence of 0.05 M 2,2-bis(hydroxymethyl)-2,2',2"-nitrilotriethanol (bis-Tris) buffer, but is changed below the pK of the bis-Tris amine, giving a maximum of 4.3 protons at pH 6.65. In 0.1 M phosphate, the maximum is increased to 6.1 protons and is shifted to pH 7.25. Addition of 1.4 mM P6-inositol lowers the magnitude of the Bohr effect and shifts its maximum to an even higher pH. At the limit of high pH (9.02), without buffer or in bis-Tris, there is a net uptake of about 0.5 proton upon oxygenation. The average heat of ionization of the Bohr groups is 5500 +/- 800 cal. Even though chloride ion has a pronounced effect on the oxygenation properties of carp hemoglobin, it has a small influence on the Bohr effect up to 0.5 M NaCl. In 5 M NaCl, the magnitude of the Bohr effect is reduced by approximately 30%., Acid base titrations give three to four oxygen-linked groups for carp hemoglobin in water; this is increased to about six groups in 2.5 M NaCl. The results suggest that carp hemoglobin is functionally versatile and may provide one way to regulate its CO2 transport via heterotropic allosteric interactions. In phosphate buffer at the pH value where carp hemoglobin is strongly cooperative, the proton release is linear with respect to ligand saturation. Lowering the cooperativity by either an increase or decrease in pH results in nonlinear relationships.

Animals↗
PubMed1979

Carp hemoglobin. V. Effects of pH and P6-inositol on autooxidation.

Autooxidation of carp hemoglobin has been measured from 4--25 degrees C with and without P6-inositol. The rate was accelerated by the increase of proton concentration and/or the addition of P6-inositol. As the rate increases the kinetics become more complex. In acidic media with P6-inositol, the autooxidation is initially rapid which becomes slower subsequently but eventually proceeds very fast. The activation energy for autooxidation is about 19 kcal. mol-1. The complicated kinetics are partly attributable to the fact that carp hemoglobin is incompletely oxygenated under these conditions and that various liganded molecules including partially oxidized species have different susceptibilities toward autooxidation.

Animals↗