Comparison of the physical properties of chemically prepared and tissue-endogenous equine apoferritins

To support the case for a biological applicability of previous experiments performed on chemically prepared apoferritin, its hydrodynamic and circular dichroic properties were compared to those of tissue-endogenous apoferritin. The molecular weights and sedimentation coefficients of the two differently prepared apoferritins were identical. Similarly, their circular dichroic spectra between 310 and 200 nm were identical. These data support the hypothesis that chemically prepared apoferritin is identical with tissue-endogenous apoferritin. Ferritins exhibited low ultraviolet CD spectra quite similar to apoferritin except amplitudes were often as much as 8% less. Apoferritin subunits, prepared by acid dissociation, did not possess the positive 292 and 286 nm bands exhibited by the native molecule, although hydrodynamically the subunit behaves as a globular protein. This suggests the presence of tryptophanyl and tyrosyl residues at the subunit contact sites. Two characteristics of the apoferritin CD spectrum were proposed as means to evaluate the quality of apoferritin preparations. These are a ratio, [theta]286 [theta]222 = -4.5 X 10(-3) +/- 0.2 X 10(-3), and the wavelength region, 258 to 262 nm, at which the near ultraviolet CD spectrum goes from a positive to a negative sense.