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Selective enhancement of ligand and flavin Raman modes in charge‐transfer complexes of sarcosine oxidase
Author(s) -
Zheng Yuangang,
Wagner Mary Ann,
Jorns Marilyn Schuman,
Carey Paul R.
Publication year - 2001
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.671
Subject(s) - chemistry , d amino acid oxidase , sarcosine , ligand (biochemistry) , raman spectroscopy , flavin group , stereochemistry , crystallography , photochemistry , oxidase test , amino acid , enzyme , glycine , receptor , organic chemistry , biochemistry , physics , optics
Monomeric sarcosine oxidase, from a bacterial source, is a 43.8 kDa flavoenzyme that catalyzes the oxidation of sarcosine ( N ‐methylglycine). The enzyme forms charge‐transfer (CT) complexes with substrate analogs such as (methylthio)acetic acid (MTA), pyrrole‐2‐carboxylic acid (PCA) and (methylseleno)acetic acid (MSA). The structure of sarcosine oxidase complexed to either of the former two ligands has been solved recently and shows that the ligands are binding close to the re face of the isoalloxazine ring. More structural detail can be adduced from Raman spectroscopic studies of these complexes. These involve collecting Raman difference data using 647.1 nm excitation, a wavelength that is in the resonance or pre‐resonance regime with regard to the CT bands. Selective intensity enhancements are observed and the difference spectra reveal a rich assortment of isoalloxazine modes and a few features due to the bound ligands. Within the CT complexes, intensity enhancement for the isoalloxazine ring vibrations is typically 1–2 orders of magnitude and is greatest for vibrations associated with the N 5 —C 4 a —C 10a —N 1 region of the ring. This identifies the region of the isoalloxazine ring that receives the charge transfer from the ligand and confirms, at the same time, that this region is a prime candidate for nucleophilic attack or electron transfer in any reaction scheme. Intensity enhancements for the ligand modes are much higher, typically a few thousand‐fold. Isotopic substitutions combined with quantum mechanical and vibrational calculations were used to identify the ligand modes showing high intensity enhancement. For MTA and MSA these are the methyl symmetric bending and methylene wag. For PCA the pyrrole ring CH deformations show the highest intensity enhancement. Copyright © 2001 John Wiley & Sons, Ltd.