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Covalently bound flavin in the NqrB and NqrC subunits of Na + ‐translocating NADH‐quinone reductase from Vibrio alginolyticus
Author(s) -
Nakayama Yuji,
Yasui Mikako,
Sugahara Kazuya,
Hayashi Maki,
Unemoto Tsutomu
Publication year - 2000
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(00)01595-7
Subject(s) - flavin group , flavoprotein , vibrio alginolyticus , flavin adenine dinucleotide , amino acid , biochemistry , chemistry , peptide sequence , threonine , peptide , stereochemistry , vibrio , biology , enzyme , cofactor , bacteria , serine , gene , genetics
Na + ‐translocating NADH‐quinone reductase (NQR) from the marine bacterium Vibrio alginolyticus is composed of six subunits (NqrA to NqrF). On SDS–PAGE of the purified complex, NqrB and NqrC subunits were found to give yellow–green fluorescent bands under UV illumination. Both the NqrB and NqrC, electroeluted from the gel, had an absorption maximum at 448 nm, and the fluorescence excitation maxima at 365 and 448 nm and the emission maximum at 514 nm. The electroeluted NqrB and NqrC, respectively, were identified from their N‐terminal amino acid sequences. These results clearly indicated that the NqrB and NqrC subunits have covalently bound flavins. The two subunits were digested by protease and then the fluorescent peptide fragments were separated by a reversed‐phase high performance liquid chromatography. N‐Terminal amino acid sequence analyses of the fluorescent peptides revealed that the flavin is linked to Thr‐235 in the NqrB and Thr‐223 in the NqrC subunits. This is the first example that the flavin is linked to a threonine residue. The amino acid sequence around the flavin‐linked threonine was well conserved between NqrB and NqrC. Identification of the flavin group is in progress.