Selective ultraviolet resonance Raman excitation of individual chromophores in nicotinamide adenine dinucleotide

Ultraviolet resonance Raman spectra (UVRRS) of reduced nicotinamide adenine dinucleotide (NADH) has been taken with ultraviolet laser excitation wavelengths (λe) of 273 nm, 330 nm and 351.1 nm. These Raman spectra have been compared with the resonance Raman spectra of the model compounds adenosine mononucleotide phosphate (AMP), with λe = 300 nm, and with reduced methyl nicotinamide (MNH), with λe = 351.1 nm, and with the classical Raman spectrum of NADH, with λe = 514.5 nm. The UVRR spectrum of NADH with λe = 273 nm resembles exclusively that of AMP while the UVRR spectra with λe = 330 nm and λe = 351.1 nm show no AMP bands but only those of MNH. The classical Raman spectrum of NADH is shown to be a superposition of bands in the resonance Raman spectra of the two chromophores but includes as well the sugar‐phosphate bands. Thus it is possible selectively to excite a UVRRS of either chromophore independently of the other. This information may prove helpful in developing techniques of UVRRS in studying NADH‐enzyme complexes since only very dilute (˜5×10−4 M) concentrations of NADH are needed for the resonant Raman spectra.