Influence of buffer system and pH on the amount of oxygen exchanged between solvent H2O and the CO2 produced in the aerobic oxidation of Cypridina luciferin catalyzed by Cypridina luciferase.

Incorporation of ¹⁸O into CO₂ was measured under various buffer conditions when the bioluminescent oxidation of Cypridina luciferin, catalyzed by luciferase, was carried out either in H₂¹⁶O medium with ¹⁸O₂ gas, or in H₂¹⁸O medium with ¹⁶O₂ gas. The results indicate that (1) the exchange of oxygen between CO₂ and solvent H₂O is significantly influenced by the kind of buffer as well as by pH, (2) the exchange of oxygen between solvent H₂O and CO₂ produced from luciferin in a neutral buffer can be reasonably well estimated from the exchange that takes place when the same amount of CO₂ gas is introduced into the same buffer by the presently employed method, and (3) in the Cypridina bioluminescent reaction, one of two oxygens of O₂ is quantitatively incorporated into the product CO₂ prior to the exchange of oxygen between CO₂ and solvent H₂O.