Introduction and a Brief Historical Overview

Hemoglin (Hb) is no doubt the most extensively studied protein, in general, and as an allosteric binding system, in particular. Although the details of its structure 

In this section we shall focus only on a few aspects of the function of this remarkable molecule. A more detailed treatment may be found in Antonini et al. (1971) and in Imai (1982). 

The Hb molecule consists of four subunits two a-subunits (each with 141 amino acid residues) and two P-subunits (each with 146 amino acid residues). The distances between the subunits in the two conformations of the Hb are shown schematically in Fig. 6.1b. The tetramer as a whole has a roughly spherical shape. Since the four subunits are not identical, one cannot expect that the four binding sites will be strictly identical. Nevertheless, in most of the theoretical treatments of the binding properties of Hb, one assumes that the sites are nearly identical, hence all of the intrinsic binding constants, as well as the correlation functions, must be understood only in an average sense, as discussed in Appendix J. 

Each of the subunits, a and P (as well as the closely related myoglobin molecule), has a prosthetic heme group to which the oxygen molecule binds. There are no covalent bonds between the subunits of Hb. The aggregate is maintained by a combination of weak direct subunit-subunit interactions as well as by indirect interactions mediated by the solvent. 

The square brackets indicate either concentration or, for oxygen, partial pressure. 

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