Comparison of experimental binding data and theoretical models in proteins containing subunits.

Publisher Summary This chapter discusses linked functions and reciprocal effects in hemoglobin. Because the components are defined thermodynamically in terms of independently variable chemical entities and, therefore, a given component may exist in any number of different forms in equilibrium with one another, these considerations show that not only do the linkage relations apply irrespective of whether the macromolecules undergo chemical change or polymerization, but also irrespective of whether the ligands themselves associate and dissociate, possibly as macromolecules. From a formal point of view the distinction between ligand and macromolecule breaks down. This principle may be useful in the application of linkage relations to antibody–antigen systems and to enzyme systems when both enzyme and substrate are proteins. Another more general, and perhaps more interesting, question is whether the dissociation process is also dependent on oxygenation, i.e., whether the protons involved are oxygen-linked. There is now strong evidence that the dissociation at acidic pH is, indeed, dependent on oxygenation.

Linked functions and reciprocal effects in hemoglobin: a second look.

Effect of organic and inorganic phosphates on the oxygen equilibrium of human erythrocytes

The secondary structure of the haemoglobin chains is similar to that of myoglobin, but some of the helical segments are more irregular and some parts of the non-helical segments have different conformations. The structure of the contacts between unlike subunits suggests that the tetramer, rather than the αβ dimer, is the functional unit of haemoglobin.

Three-dimensional Fourier Synthesis of Horse Oxyhaemoglobin at 2.8 Å Resolution: The Atomic Model

Tannins are phenolic compounds of widespread occurrence in higher plants. They have complicated structures that have only recently been unraveled by natural products chemists. They are not known to have any physiological function. So what do they do? Examination of their structures and consideration of several possible roles, especially as defensive compounds against plants' enemies, allows much speculation. It is proposed that the enormous structural heterogeneity and natural division of tannins into two broad classes, the condensed and hydrolyzable, has important ecological consequences. It is argued that their structures suggest strong specificities for a variety of target molecules including proteins, digestive enzymes, and polysaccharides. These specificities insure mainline defense against plant enemies, but are nevertheless subject to the coevolutionary "arms race" (Feeny 1976). The idea that condensed tannins are reserved primarily for defense against microbes and pathogens, while the hydrolyzable...

Tannins: does structure determine function? An ecological perspective

Publisher Summary This chapter describes hemoglobin and myoglobin. Hemoglobin and myoglobin are, among all proteins, ones that have been, and are, most actively studied; an enormous number of papers have been published over the past hundred years on all aspects of their properties and behavior. The study of these proteins has gone beyond the interest in their physiological role as oxygen carriers because they represent ideal models for investigating the properties of proteins in general, especially of enzymes. Correspondingly, current knowledge of the structure and function of hemoglobin and myoglobin is far greater than that available for any other protein. In spite of this, however, many questions still remain unsolved regarding the exact molecular mechanisms involved in the function of these proteins. Before discussing the properties of respiratory heme proteins, it is necessary to briefly describe some properties and reactions of their prosthetic group, mainly because the characteristic physiological functions of these proteins arise from the intrinsic reactivity of the heme.

Antonini E

Papers

Hemoglobin and myoglobin.