P50 (pressure)
In
The concept of p50 is derived from considering the fractional saturation of a protein by a gas. Imagine myoglobin, a protein which is able to bind a single molecule of oxygen, as per the reversible reaction below, whose equilibrium constant K (which is also a dissociation constant, since it describes a reversible association-dissociation event) is equal to the product of the concentrations (at equilibrium) of free myoglobin and free oxygen, divided by the concentration of myoglobin-oxygen complex.
The fractional saturation YO2 of the myoglobin is what proportion of the total myoglobin concentration is made up of oxygen-bound myoglobin, which can be rearranged as the concentration of free oxygen over the sum of that concentration and the dissociation constant K. Since diatomic oxygen is a gas, its concentration in solution can be thought of as a partial pressure.
From defining the p50 as the partial pressure at which the fractional saturation is 50%, we can deduce that it is in fact equal to the dissociation constant K.
For example, myoglobin's p50 for
References
- ^ P 50 – definition of P 50 in the Medical dictionary – by the Free Online Medical Dictionary, Thesaurus and Encyclopedia. Medical-dictionary.thefreedictionary.com. Retrieved on 2013-10-22.
- ^ Oxygen/Hemoglobin Archived 2010-05-23 at the Wayback Machine. Lexingtonpulmonary.com. Retrieved on 2013-10-22.
- S2CID 19110159.
- ISBN 978-1-259-90388-5.