KERR EFFECT OPTICAL DISPERSION OF HEMOGLOBIN . A MOLECULAR INTERPRETATION

Kerr constant increments of horse oxy and met hemoglobin are reported at 546, 436, and 365 mμ. The data are interpreted in terms of theoretical estimates of the molecular dielectric and optical parameters. Dielectric parameters were calculated by extensions of the Kirkwood-Shumaker and Tanford-Kirkwood theories, using site coordinates from a model of horse oxy hemoglobin. The contribution of the heme spectrum to the polarizability anisotropy was calculated from the Kramers-Kronig relation and geometrical information. The theoretically predicted Kerr constant increments were found to be very sensitive not only to the heme orientations and small x, y splittings of the Soret and visible bands, but also to the details of the proton-fluctuation anisotropy. Significant pH dependence was also predicted. The theory and data are in qualitative agreement, although more extensive experimental results are desirable.