The tetramer (biological assembly) is generated by the crystallographic twofold axis -x,y,-z+1/2 and translation by one unit cell length along x (alternative by the equivalent axis parallel to y located at 1/2x, 1/4z)
SEQUENCE RESIDUES MET 63, TYR 64 AND GLY 65 AUTOCATALYTICALLY FORM THE CHROMOPHORE NRQ LABELLED AS ...SEQUENCE RESIDUES MET 63, TYR 64 AND GLY 65 AUTOCATALYTICALLY FORM THE CHROMOPHORE NRQ LABELLED AS RESIDUE 65 IN THE COORDINATES.