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interconverting
between oxyHbA and deoxyHbA, "squeezing"
oxygen out or "soaking" it up in the process.
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- By the sponge analogy,
Ya is
a measure of how much
oxygen Hb sponge binds.
- Since O2 binding is a dynamic
process, Hb is an "oxygen sponge" in that it continuously is either being soaked
with oxygen
(in the oxygen-rich environment of the lungs) or "squeezed"
forcing it to release of some or all of its bound oxygen (in oxygen
starved capillaries that penetrate oxygen-consuming tissues).
- In other words, Hb is being forced to
"expand" or "contract" between its oxy-
and deoxy-conformations and in the process
it binds or releases oxygen.
- Just as a sponge can can hold only so much water, depending on
its size and
elasticity, Hb can bind only so much oxygen, 4 O2 molecules
for each Hb molecule to be exact.
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