Biology Reference
In-Depth Information
62
al.
(1955) in the Hill's plot, these three equilibrium constants will be
changed slightly.
OTHER STUDIES ON HEMOGLOBIN
We have only reviewed three of the relatively simple models on equilibrium
saturation of hemoglobin with oxygen. There are many other models, e.g.
Adair's (1925), Koshland's (1966). etc., proposed during the past century.
In addition, this protein also transports carbon dioxide, and has many
additional interesting properties.
Over the years, numerous studies have been carried out on its kinetic
properties, replacement of iron by other transition elements, effects of pH,
binding of small molecules, genetic mutants, etc., just to name a few. A
close collaboration between experimental measurements and theoretical
models plays vital roles in all of these studies. There are also many diseases
associated with hemoglobin abnormalities, e.g. Hb Kansas, Hb Yakima, Hb
Zurich, Hb S, Hb Lepore, and thalassemia, persistence of fetal chain,
etc. Only recently, specified amino acid residue changes have been used to
study the detailed molecular mechanisms of hemoglobin functions (Bettati
et al.
, 1998; Tsai
et al.
, 2000).
2,3-DIPHOSPHOGLYCERATE
This small molecule is highly concentrated inside our red blood cells. Each
hemoglobin molecule binds one molecule of 2,3-diphosphoglycerate. Its
presence is essential to the S-shaped hemoglobin saturation curve. Perutz
(1970) has reasoned that it binds tightly to the of deoxy-
hemoglobin or the T-state. On transition to oxy-hemoglobin or the R-state,
2,3-diphosphoglycerate drops out. Whether it binds to the two
symmetrically (Arnone, 1972) or asymmetrically (Pomponi
et al.,
2000)
remains uncertain.
OTHER ALLOSTERIC PROTEINS AND ENZYMES
Conformational changes of proteins due to the binding of small molecules
occur frequently in various biochemical reactions. Since the first
description of this phenomenon, known as allosteric regulation, in 1963 by
Monod
et al.
, numerous papers are published yearly about various proteins
