title: Optically detected magnetic resonance of the phosphorescent bases of Escherichia coli valine-specific transfer ribonucleic acid.
abstract: Phosphorescence spectroscopy and optical detection of triplet state magnetic resonance (ODMR) spectroscopy have been used to characterize bases that contribute to the phosphorescence emission of Escherichia coli valine-specific transfer ribonucleic acid. When it is excited with 335-nm light, a short-lived phosphorescence with an origin near 435 nm is observed and is assigned to 4-thiouridine (s4U) at position 8 of the tRNA sequence. With excitation at 290-300 nm, a structured, long-lived phosphorescence is observed with an origin near 380 nm, in addition to the s4U phosphorescence. Comparison was made of the phosphorescence and ODMR spectra between Mg2+-containing and Mg2+-free tRNA samples. The s4U phosphorescence of the Mg2+-containing sample is more structured, and the peak is blue shifted relative to the Mg2+-free sample. Both samples give a single low-frequency (ca. 2.9 GHz) ODMR signal, but the high-frequency signal region (ca. 19-20 GHz) is structured. The Mg2+-containing sample has a partially resolved group of lines centered at 19.3 GHz, whereas the Mg2+-free sample has two broad bands centered at 19.2 and 20.0 gHz. The differences are attributed to effects of Mg2+ on the tRNA conformation. The ODMR signals observed by monitoring the long-lived phosphorescence are assigned to a pyrimidine nucleoside, possibly 5-(carboxy-methoxy)uridine in the anticodon.
mesh_terms: D001483:Base Sequence; D004926:Escherichia coli / Q000032:analysis*; D007700:Kinetics; D008163:Luminescent Measurements; D009682:Magnetic Resonance Spectroscopy; D009690:Nucleic Acid Conformation; D012346:RNA, Transfer, Amino Acyl / Q000032:analysis*; D013891:Thiouridine
chemical_list: D012346:RNA, Transfer, Amino Acyl; D013891:Thiouridine