Significance of the upward curvature

Plotting (lo /1 -1) / [O2] as a function [O2] should allow to calculate the values of the two constants. However, one can notice that it is impossible to obtain values for the two constants. In fact, only dynamic quenching constants were obtained, equal to 13.2 and 12.3 M at 35 et 15°C, respectively. This is probably due to the fact that one of the two constants is equal to zero. In the absence of iron, oxygen molecules do not bind to myoglobin, which eliminates the static component. 

This phenomenon is referred as sphere of action within which the probability of quenching is unity. The sphere of action is characterized by a volume v. Determination of this volume is possible with Eq. 9.5 (Frank and Vavilov, 1931) 

V is the volume occupied by one mole of the two interacting entities, oxygen and porphyrin. 

The volume v of the sphere of action or the volume occupied by one molecule is equal to  

V can be determined from the asymptote drawn at low oxygen concentration (Fig. 9.20, slope 1). In fact, the asymptote supposes that exponential factor is absent and thus the Stem-Volmer plot is linear and can be described with the classical Stern-Volmer Equation (Eq. 4.6). 

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