Hemoglobins oxygen-linked acid groups

Constants of Oxygen-linked Acid Groups in Horse Hemoglobin at US and an Ionic... 

If it is assumed that the hemoglobin molecule has four identical hemes with two oxygen-linked acid groups per heme, Eq. (22) becomes... 

The assumption that the dissociation of the two oxygen-linked acid groups are independent of each other is not necessary for a quantitative treatment of the Bohr effect. Alberty (1955) derived an expression of AX for the more general case where the dissociation of these two acid groups are not independent of each other. His expression has the same functional dependence on [H ] as Wyman s. In particular, for hemoglobin with K2IK1 1 and 1, Alberty s numerical results are... 

Variation of pH has only a small effect on the dissociation equilibrium of oxymyoglobin (Theorell, 1934b). The observed pH dependence can be accounted for by the assumption of one oxygen-linked acid group (Wyman, 1948 George and Hanania, 1955). The effect of pH on the dissociation equilibrium of carboxymyoglobin is more pronounced (Chiu and Spencer, 1960), but still much less than oxy- or carboxy-hemoglobin. 

Wyman and collaborators presented conclusive experimental evidence that Conant s assumption was justified—that imidazole residues of histidine must be linked to the iron in hemoglobin. The differential acid-base titration data of German and Wyman (30) between hemoglobin and oxyhemoglobin were taken as the base for calculations by Wyman (92), and these established the existence in hemoglobin of two acid groups (pK 5.25 and 7.81). On oxygenation, these values shifted to 5.75 and 6.80. 

The Coryell-Pauling hypothesis was based on Wyman s observation that the heat of dissociation of the oxygen-linked acid goups in hemoglobin, 6.5 kcal./mole, is characteristic of imidazole group (Wyman, 1939), However, Wyman s identification of the imidazole groups from the... 

The standard enthalpies of the dissociation reactions are those determined by Antonini, et al (11) for horse hemoglobin. Their p fs are based on the assumption that the oxygen-linked groups are independent. However, pKi and p/fa in equation 14.2-1 are the usual thermodynamic p fs independent of any assumptions. Actually some of the acid dissociations are cooperative, which indicates that they are not independent. The p s used in the current calculations were obtained using... 

Pyridoxal phosphate is a required coenzyme for many enzyme-catalyzed reactions. Most of these reactions are associated with the metabolism of amino acids, including the decarboxylation reactions involved in the synthesis of the neurotransmitters dopamine and serotonin. In addition, pyridoxal phosphate is required for a key step in the synthesis of porphyrins, including the heme group that is an essential player in the transport of molecular oxygen by hemoglobin. Finally, pyridoxal phosphate-dependent reactions link amino acid metabolism to the citric acid cycle (chapter 16). 

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