Haemoglobin
Structure of
normal haemoglobin:
- Hct 40-45 %
- male: 16 gms haemoglobin per 100 ml whole
blood
- female: 14 gms haemoglobin per 100 ml whole
blood
- 1 gm Hb combines with 1.4 mls O2
è 21
ml O2 per 100 ml blood (male)
- Haemoglobin
is made up of the protein globin boundto the red pigment heme.
- Haemoglobin
consists of 4 polypeptide chains: two alpha and two beta, each with a heme
group.
mechanism of
oxygen binding
- When
oxygen binds to iron, the Hb assumes a new three dimensional shape called oxyhemoglobin [becomes bright red].
- When
oxygen dissociates from Hb. the Hb ressumes its former shape becoming deoxyhemoglobi (reduced Hb)
[becomes dark red].
- Oygen
does not combine with the two positive valences
of the ferrous iron in the Hb molecule. Instead it binds loosely with one of the six
‘coordination’ valences of the Fe atom. This is an extremely loose bond so
that the combination is easily reversible.
Furthermore, the oxygen is not carried in an ionic oxygen but is carried
as molecular oxygen where, because of its loose, readily reversible
combination, it is released into the tissue fluids in the form of
dissolved molecular oxygen.
- When
the PO2 is high, as in the pulmonary capillaries, oxygen binds
with the Hb. When the PO2 is low, as in the tissue capillaries,
oxygen is released from the Hb.
K. C. Potger
Copyright © 2001