Effects of Glutamate Dehydrogenase Enzyme on the SERS Spectra of Nicotinamide Adenine Dinucleotide on a Gold Electrode

Abstract

Near-infrared Fourier transform Raman spectroscopy was used to study the SERS behaviors of nicotinamide adenine dinucleotide (NAD) in a solution containing Glutamate dehydrogenase enzymes. It was found that the SERS spectra of NAD adsorbed on a gold electrode should be largely changed by addition of glutamate dehydrogenase (GDH) in the electrolyte solutions. The potential dependence of the SERS revealed that, in an adequate negative potential region, NAD adsorbed on a gold electrode can be combined with the enzyme to a certain extent. The SERS spectra of NAD/GDH exhibit some different properties from those shown for normal SERS spectra of NAD alone in two aspects: (1) The existence of the enzymes led to decrease or disappearance of several strong bands under open circuit conditions. The reductions of the SERS bands are quite consistent with the changes of normal Raman spectra of NAD in combination with some NAD-dependent dehydrogenase in solutions. The protonation of the adenine moiety was proposed to explain this SERS behavior. (2) Several new bands, some of which can be attributed to the backbone peptide of the enzyme, appeared and increased in intensity with a negative shift of the electrode potential. The appearance of the new bands was attributed to the close approach of the active site of the enzyme induced by the coenzyme preadsorbed on the surface.

Structural features of the adenosine conjugate in means of vibrational spectroscopy and DFT

“…The appearance of this mode suggests that ribose is in intimate contact with the metal surface through the OH groups, and rather weak interactions between the pentose ring and the surface that has been previously reported [20][21][22][23]. It is the most likely that other bands arising from ν(OH) of ribose are hindered by the broad band at around 3300 cm , which are attributed chiefly to the bending modes of COH and CCH, and the stretching modes of CC and CO bonds according to our calculations (see Table 2).…”

“…Until now, vibrational interpretation of this class of compounds has been carried out by using characteristic frequency groups only [13][14][15]. Also the possible mechanism of adsorption of all the compounds studied here on different silver and gold surfaces were proposed [13,[16][17][18][19][20][21][22][23][24][25].…”

“…The allocation of the SERS bands to the normal vibrations was done referring to DFT calculations mentioned-above. Also, previously reported assignments of SERS bands reported for adenine [16][17][18], adenosine [19][20][21][22], D-ribose [23] and benzo-5-crown ether [13,24,25] . Below 1150 cm -1 there is a number of very weakly enhanced bands.…”

“…All In addition, it has been previously suggested [16][17][18][19][20][21][22] that the SERS band at ca. 1330 cm -1 was attributed to the stretching vibration of the C 5 -N 7 bond.…”

“…Also, all the SER spectra of adenine and adenosine exhibit a strong band near 730 cm -1 , which has been attributed to the "breathing" mode of the adenine ring. This vibration is much stronger enhanced for vertical orientation of adenine than for flat (parallel) position of this ring [16][17][18][19][20][21][22]. Since, as shown in Fig.…”