The photochemical formation of a quickly reacting form of haemoglobin

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Abstract
When carboxyhemoglobin is broken down by the action of light the newly formed reduced hemoglobin has, for a brief period, a higher rate of reaction with carbon monoxide or oxygen than reduced hemoglobin of greater age. The observed reaction is influenced by pH and by -SH reagents. At neutral pH little quickly-reacting hemoglobin (Hb*) is formed. If p-chloromercuribenzoate is added almost all the reduced hemoglobin formed is Hb*). At alkaline pH the chief product of photolysis is Hb*) even in the absence of p-chloromercuribenzoate. At alkaline pH Hb* reverts spontaneously to ordinary hemoglobin with a velocity constant of about 200 sec."1 at 1[degree]. The second-order velocity constant for the combination of Hb*with carbon monoxide is 1*8 x 106 M-1 sec.-1 at 1[degree] and the activation energy 5 6 kcal. The bearing of these results on the use of flash photolysis in the study of hemoglobin kinetics is discussed.