Oxygen binding by myoglobin (Mb)

Since O 2 is a gas, we can replace the concentration [O 2 ] by partial pressure p(O 2 )

Exercise 2: Calculate the slope of the saturation curve at p(O 2 ) = 0. Plot the slope dY/d[p(O 2 )] as a function of p(O 2 ) p(O 2 ) [Torr]Y [%] Exercise 1 Calculate the saturation curve for oxygen binding to myoglobin. Disociation constant of the MbO 2 complex at 37 °C, pH = 7, p = 760 Torr: K d = 2.8 Torr

At p(O 2 ) = 0  Čím silnější afinita mezi Mb a O 2, tím strmější křivka v bodě 0;0

 Slope of the saturation curve decreases with p(O 2 )

Saturation curve for hemoglobinu does not correspond to a single reversible reaction  Binding of O 2 to one subunit of hemoglobin increases the affinity for O 2 of the other subunits „Cooperative effect“

Cooperativity of oxygen binding by the 4 subunits of hemoglobin: In deoxygenated form, the 4 subunits stabilize mutually the domed conformation.  The oxygen affinity of unloaded hemoglobin is smaller than that of individual subunits. Oxygen binding to one subunit of hemoglobin favors the planar form at neighboring subunits  fully loaded hemoglobin has an affinity similar to that of an individual subunit.

Effect of CO 2 on oxygen afinity of hemoglobin: „Bohr-Effect“ In muscles, where metabolic activity produces CO 2, amino groups of certains amino acids are transformed to carbamate: The liberated H + protonates histidine residues: At subunit interfaces salt bridges are formed: These salt bridges favor the domed conformation  favor O 2 release  CO 2 favors release of O 2 which is then taken up by myoglobin

In muscles: High CO 2 concentration favors domed conformation  favors O 2 release In bronchi: Low CO 2 concentration favors planar conformation  favors O 2 binding