THE ENERGETICS OF PHOTOSYNTHESIS 63 



In contrast to photosynthesis, the dissociation of iron carbonyl compounds 

 is reversible 



[FejCO ^ [Fe] + CO 



In darkness the reaction may proceed from left to right. In light it proceeds 

 only from left to right. Consequently, in illuminated solutions of carbon 

 monoxide hemochromogen and carbon monoxide ferrocysteine there are 

 three parallel reactions — two dark reactions and one photochemical reaction. 

 In the case of carbon monoxide hemoglobin four dark reactions and one 

 photochemical reaction can be differentiated, as the two following dark 

 reactions also occur: 



[FejCO + 02^ [FeJOo + CO 



The experiments are carried out with the differential manometer, both 

 vessels containing the solution of the iron carbonyl compound. The gas 

 phases have a certain CO partial pressure. After equilibrium has been 

 reached in the dark, one of the vessels is illuminated with light of known 

 wave-length and intensity. Upon illumination, CO is produced and the 

 pressure rises to constant value. When the light is removed, the pressure of 

 the photochemically liberated CO falls to zero, as, in the dark, the equilib- 

 rium at the beginning of the experiment nmst be restored. From the speed 

 of this return to zero can be calculated how many mole CO per min re-react. 

 These are n mole. Since the number of mole quanta q which are absorbed 

 per min is also known, the quantum yield can be calculated from equation 3. 



Lautsch et al. (3, 15) made compounds of certain peptides with active 

 groups from the hemin series. These served as oxidase models in their 

 studies. Photochemical cleavage of the CO compounds of these synthetic 

 substances also gave a value of 1 for the quantum requirement. 



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