Is there an optimal P₅₀ of haemoglobin?

Abstract

SummaryThe cf;f;.ct ( Key wordsHaernoglobin; half-saturatio? pressure, oxygen transport, oxyhaemoglobin dissociation curve. Pso. Oxygen; oxygen-haemoglobin affinity.Many factors affect the oxygen supply to the tissues. These include the pattern of the capillary network, the magnitude and the distribution of the capillary flow, the presence of oxygen stores (myoglobin), diffusion rates, and the instantaneous oxygen consumption; but essentially the oxygen supply is determined by the arterial oxygen tension and the shape and the position of the oxygen-haemoglobin association/dissociation curve. A right-shift, expressed by an increase of the Pso (tension at 509, saturation of haemoglobin). usually enhances oxygen release. whereas a left-shift represents an increase in oxygenhaemoglobin affinity and impedes the unloading of oxygen. Stimulated by a short article written by Tien, I the quantitative effects that different Pso values would theoretically exert on oxygen release were studied. and the conditions under which the dissociation curve of healthy adults with a Pso of 3.53 kPa is most appropriate were determined. This study started because the author was intcrested to discovcr the effects outlined above. The results seem of sufficient general educational intercst to justify a wider audience and the results are presented in order LO achieve this. MethodsThe calculations are based on Hill's equation

The Cooperativity of Human Fetal and Adult Hemoglobins is Optimized: A Consideration Based on the Effectiveness of the Bohr Shift

“…Together with the previous conclusion that the position of the OEC for fetal Hb is optimized for O 2 delivery (Sold, 1982;Willford et al, 1982;Kobayashi et al, 1996), the present result indicates that the position of the fetal Hb seems to be well adapted to maintaining the effectiveness of the Bohr shift at high levels at both O 2 loading and release sites. The higher effectiveness of the Bohr shift at the site of O 2 release relative to that at the O 2 uptake may be adequate for preventing the accumulation of proton and CO 2 in the fetal tissues.…”

Significance of Affinity and Cooperativity in Oxygen Binding to Hemoglobin of Horse Fetal and Maternal Blood

“…The amount of O 2 transported at physiological P 50 was slightly lower than that of the maximum value at optimal P 50 value. In human fetal Hb, it is well known that the physiological P 50 of human fetal Hb is close to the optimal P 50 (Itoh et al, 2001;Sold, 1982;Willford et al, 1982). Therefore, the O 2 tranasport efficiency of horse fetal blood is not so high as that of human fetal blood.…”

A New Look on the Position of the Oxygen Equilibrium Curve of Human Adult Hemoglobin at Rest and during Exercise with Special Reference to the Effectiveness of the Bohr Shift

“…As shown by the broken line, the O 2 transported by Hb increased gradually with increases in P 50 , reaching its maximal value at P 50 of 62 torr. The P 50 value that gives the maximal O 2 transport may be called the "optimal P 50 for O 2 transport" (Sold, 1982;Willford et al, 1982). At the physiological P 50 value for adult whole blood (P 50 = 27 torr), the O 2 transported by Hb was relatively low (∆S (100-40) = 0.22).…”