Real light emitter in the bioluminescence of the calcium-activated photoproteins aequorin and obelin: light emission from the singlet-excited state of coelenteramide phenolate anion in a contact ion pair

Fluorescent properties of the phenolate anion and the amide anion of coelenteramide analogues in ion pairs with various counter cations were systematically investigated to confirm that the singlet-excited state of coelenteramide phenolate anion in a contact ion pair is the real light emitter in the bioluminescence of aequorin and obelin.