E3d was )ess thermostable than E3c; E3d and E3c lost half of their original activities upon incubations for 30 min at 790C and 900C, respective]y. Heat treatment of E3d raised the fluorescence ;ntensities of Trp residue, intrinsic FAD, and extrinsic 8-anilinonaphthalene-1-sulfonate. E3d lost FAD, and inactive E3d polypeptides were aggregated. The sulfonate bound to the aggregate became notably ...