The slope of the oxygen equilibrium curve (OEC) of mammalian-hemoglobin (Hb) is maximized at
S (oxygen saturation) value of 0.38, and the slope of the
S vs.
P/
P50 (
P is partial oxygen pressure;
P50 is
P at
S = 1/2) plot at a
P/
P50 value of 1 is one-forth that of the Hill-coefficient (
n). OECs of mammalian Hbs are designed to have an identical optimal
P50 value for O
2 delivery and the effectiveness of the Bohr shift (shift of OEC upon pH changes) at O
2 loading site. This fact is favorable for uptake and delivery of maximum amount of O
2 for fetal blood. To have the identical optimal
P50 value for O
2 delivery and for the efficiency of the Bohr shift, the relationship,
PaO
2/
PvO
2 = ((
n + 1)/(
n − 1))
2/n, is required to hold, where
PaO
2 and
PvO
2 are
P for arterial and venous bloods, respectively.
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