Effects of inositol hexaphosphate on the Bohr effect induced by CO2 and fixed acids in chicken hemoglobin

Red cell organic phosphates and Bohr effects in house sparrow blood

CO2 and fixed acid Bohr effects (d log PO2/d pH) were determined for fresh whole blood of adult house sparrow (Passer domesticus) at 35, 41 and 45 degrees C. At each temperature, the effects of titrating blood with CO2 at constant base excess (CO2 Bohr effect) were similar at P50 (35 degrees, -0.48; 41 degrees, -0.49; 45 degrees, -0.49). The CO2 Bohr slopes were also reasonably saturation independent between 10 and 90% S. Fixed acid Bohr values, determined by titrating sparrow blood with HCl and NaHCO3 at 4% CO2, were significantly less than the corresponding CO2 coefficients at half saturation (35 degrees, -0.43; 41 degrees, -0.39; 45 degrees, -0.41). The difference between CO2 and H+ Bohr effects, assumed here to represent carbamino CO2 binding to hemoglobin, decreased in magnitude with increasing saturation at each temperature. Inositol pentaphosphate (IPP, 3.1 mumol/ml RBC) and ATP (7.7 mumol/ml RBC) were the major organic phosphates present in Passer erythrocytes. CO2 and organic phosphates are known to complete for common binding sites on the Hb molecule. Because of IPP's strong binding affinity and high concentration in most avian red cells, carbamate formation is generally suppressed in bird blood. The presence of a small but significant specific CO2 effect in Passer blood may indicate that one or both sparrow isohemoglobins has reduced affinity for IPP and/or ATP, permitting CO2 to compete more effectively in Hb-carbamate formation.

Fixed acid and carbon dioxide Bohr effects as functions of hemoglobin-oxygen saturation and erythrocyte pH in the blood of the frog, Rana temporaria

Using a thin film, dynamic recording technique, the pH sensitivity of the oxygen equilibrium (Bohr effect) of whole blood in the frog Rana temporaria, and its dependence on CO2 and fixed acids and on plasma and erythrocyte pH values were measured. Under standard conditions (20 degrees C, PCO2 = 14.7 mm Hg, pH = 7.65) the oxygen equilibrium could be described by a P50 value of 38 mm Hg and n50 of 1.8 Hill plots of the oxygen equilibria showed increased cooperativity in oxygen binding with increasing saturation (n20 congruent to 1.2, n80 congruent to 4.0). Values of fixed acid and CO2 Bohr factors (phi AH and phi CO2, respectively) were similar at specific saturations (S20, 50, 80) but showed saturation dependence with high values occurring at high saturation. The same statements also hold for the intracellular Bohr factors (derived from the relation between blood P50 and erythrocyte pH) although the values of both phi AH and phi CO2 now were greater than those related to blood pH.

Oxygen affinity of blood of adult domestic chicken and red jungle fowl

Respiratory properties of blood from adult domestic chicken (White Leghorn) and red jungle fowl (Gallus gallus, ancestor of domestic breeds) at 41 degrees C were investigated. Oxygen affinity was the same in blood of chicken and jungle fowl (P0.5 46.7 Torr at pH 7.5, 41 degrees C, PCO2 about 30 Torr). The Hill coefficient, nH, increased from 2 at oxygen saturation 0.1 to a maximum of 4.11 at saturation 0.8. Leghorn fixed acid and CO2 Bohr coefficients were -0.51 and -0.53, with little variation over the saturation range 0.15-0.95, indicating negligible specific CO2 effect. An nH value of greater than 4 may indicate polymerization of deoxyhemoglobin, comparable to that which occurs in sickle cell hemoglobin. A biphasic equilibrium curve shape (hump at the low end of the oxygen equilibrium curve) was noted in blood having some degree of hemolysis. Factors that may have contributed to the differences between previous investigations of chicken oxygen affinity are discussed.

Root effect induced by CO2 and by fixed acid in the blood of the eel, Anguilla anguilla

The decrease in O2 capacity with decreasing pH (Root effect) was studied in eel blood in which pH was varied in the range 5 to 9 both by addition of acid or base (fixed-acid Root effect) and by varying PCO2 (CO2 Root effect). Hemoglobin-bound oxygen was independent of PO2 above 150 Torr and was thus referred to as O2 capacity (O2cap). At pH below 8.5, O2cap decreased sigmoidally with pH to attain, below a pH of 6.0, a value which, at 15 degrees C, averaged about 48% of the maximum O2cap, measured above pH 8.5. At 25 degrees C, this reduction was even more pronounced. For pH above about 6.5 the decline in O2cap was independent of whether the pH was diminished by CO2 or by fixed acid. Below pH 6.5, however, the CO2 Root effect exceeded the fixed-acid Root effect. Below pH of 7.5, the buffer value of true plasma increased with declining pH and attained a negative value in the range where CO2 exerted a specific action on the Root effect.