Horse hemoglobin

Fig. 8. Oxygen equilibrium curves of caiman and horse hemoglobin with and without C02. C0] = 40Torr, 25°C, I = 0.2 M, pH 7,2 for caiman (60), pH 7.4 for horse (104).

FIGURE 2.21 Effect of ionic strength on the solubility of horse hemoglobin. [Graph reconstructed from E. J. Cohn, Chem. Rev., 19, 241 (1936).]... 

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... 

Pauling and Corey (1599) made the point that under certain conditions globular proteins can be converted to forms similar to j8-keratin, and on this basis they proposed the a-helix as a basic feature in fRe structure. Perutz s x-ray work (256, 1614) shows that parts of horse hemoglobin may have this structure. Ambrose and Elliott (35) present some IR work on globular proteins in a paper which particularly stresses the functions of H bonds. 

FIGURE 7.7. Methods of mounting crystals, (a) A crystal mounted in a glass fiber, as used for a small-molecule crystal that does not decompose on exposure to air. (b) Diagram of the mounting of a crystal in a capillary tube, (c) and (d). A crystal of a chemically modified horse hemoglobin enclosed with mother liquor in a thin walled glass capillary. (Courtesy J. J. Stezowski). 

Problem 36.22 (a) Horse hemoglobin contains 0.335% Fe. What is the minimum molecular weight of the protein (b) Osmotic pressure measurements give a molecular weight of about 67,000. How many iron atoms are there per molecule ... 

The classic example is monoclinic C2 horse hemoglobin studied by Max Perutz. In this crystal form it was known from density measurements that the C2 unit cell contained two entire molecules of hemoglobin. There are four asymmetric units in a C2 unit cell, however, as the International Tables show. Thus one-half of a hemoglobin, to satisfy space group symmetry, had to be related to the other half by a twofold axis. By this means horse hemoglobin was shown to possess a perfect twofold axis of symmetry well before it was demonstrated by any other means. 

In contrast to the high a-helix contents of sperm whale myoglobin or horse hemoglobin, a respiratory hemoprotein from Chironomus thummi had about one third less a-helix content as estimated from its rotation at 233 nm (153) lamprey hemoglobin also indicated less a-helix content (179, 144). 

The following are the percentages of iron and sulfur (other than disulfide sulfur) found in horse hemoglobin ... 

The most accurate and extensive data on the oxygen equilibrium are those obtained by Ferry and Green for horse hemoglobin in phosphate and borate buffers. Ferry and Green remarked that their curves of y (the ratio... 

The complete amino acid sequences (primary structure) of hemoglobins can, in principle, be determined by methods currently available. Although detailed studies of the primary structure of human and horse hemoglobins are in progress in several laboratories, the methods are so laborious that complete sequences have not yet been established. Important questions in the realm of genetics and evolution require the immediate examination of the structure, primary and other, of... 

A detailed study of horse hemoglobin has shown that the alpha chains differ from those of human hemoglobin by about 18 amino acid substitutions, as do also the beta chains of the two hemoglobins. If we accept 130,000,000 years as the time that has passed since the evolutionary lines of horse and human separated, as estimated by paleontologists, we conclude that each chain has on the average suffered an evolutionarily effective mutation every 14.5 million years. We may then use this value to discuss other evolutionary epochs. 

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