Abstract The interactions between zinc-free insulin and vanadium compounds, NaVO_3, VO(acac)_2 and VO(ma)_2, have been in-vestigated by fluorescence spectroscopy, circular dichroism (CD) and Fourier-transformed infrared (FT-IR) spectroscopy. The resultsshowed that binding of vanadium compounds produced a static quenching of the intrinsic fluorescence of insulin. The apparent associationconstants were determined to be (0. 17±0. 01)×10~4 L·mol~(-1) for NaVO_3, (2. 8±0. 2)×10~4 L·mol~(-1) for VO(acac)_2, and (4. 0±0. 1)×10~4 L·mol~(-1) for VO(ma)_2, respectively. The light scattering intensity of insulin decreased upon incubation with the vanadium com-pounds, suggesting the disaggregation of insulin. The attenuation of the band at 273 nm of insulin CD spectra also supported the disaggre-gation of insulin observed above. A new band at 1650 ～ 1653 cm~(-1) appeared in the FT-IR spectra of insulin upon incubation with the vana-dium compounds, indicating the formation of an α-helix structure at B (9- Abstract The interactions between zinc-free insulin and vanadium compounds, NaVO_3, VO (acac) _2 and VO (ma) _2, have been in-vestigated by fluorescence spectroscopy, circular dichroism (CD) and Fourier- transformed infrared (FT-IR) The resultsshowed that the binding of vanadium compounds produced a static quenching of the intrinsic fluorescence of insulin. The apparent association constants were determined to be (0.17 ± 0.01) × 10 -4 L · mol -1 for NaVO 3 , (2. 8 ± 0. 2) × 10 ~ 4 L · mol -1 for VO (acac) 2 and (4 ± 0 1) × 10 4 L · mol -1 ) for VO (ma) _2, respectively. The light scattering intensity of insulin decreased upon incubation with the vanadium com-pounds, suggesting the disaggregation of insulin. The attenuation of the band at 273 nm of insulin CD spectra also supported the disaggre-gation A new band appeared at 1650 ~ 1653 cm -1 in the FT-IR spectra of insulin upon incubation with the vana-dium compounds, indicating the formation of an α-helix structure at B (9-