On the quantitation of light emission from cytochrome c in the low quantum yield limit

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Abstract
A method for the quantitation of light emission is presented which uses the Raman scattering cross section of water as a reference. The method is successfully applied to systems having a known quantum yield, thus providing an independent check of Raman cross‐section measurements. A very weak incoherent emission from the ferrocytochrome c system is quantitated (Φ=3.6×10−6) and interpreted using a simple kinetic model which is consistent with the quantum mechanical treatment. The quantum yield measurements imply that the excited state (S1) lifetime of the ferrocytochrome is on the order of 0.2 ps, while the lifetime of the ferricytochrome is deduced to be much shorter. The implications of these measurements concerning the magnitudes of the excited state (S1, S2) damping factors in ferrocytochrome c are also discussed.