THE ANOMALOUS MOSSBAUER FRACTION OF FERRITIN AND POLYSACCHARIDE IRON COMPLEX (PIC)

Mossbauer studies of the ubiquitous protein molecule ferritin and its synthetic ''biomimic'' polysaccharide iron complex (PIC) exhibit an an omaly in the Mossbauer spectrum wherein the recoil free fraction orf-f actor has a sharp drop with respect to temperature as the temperature rises above 30 K for mammalian ferritin and 60 K for PIC. The anomaly coincides with the disappearance of hyperfine splitting, which is due to superparamagnetic relaxation above the blocking temperature. Differ ent absorbers were used to experimentally investigate the effect of ab sorber thickness on the Mossbauer spectrum. The anomaly persists for t hin absorbers. Also, spectra treated with FFT procedures to eliminate the thickness effect still exhibit this anomaly. Motion of the core wi th respect to the protein shell was also eliminated as a possible sour ce for this phenomenon, by comparing the Debye temperature obtained fr om the temperature dependence of the f-factor and the isomer shift. A comparison of the magnetic anisotropy constants from magnetization stu dies with those obtained by relating the hyperfine field H of the Moss bauer spectra to the fluctuations of the magnetization imply that the ferritin and PIC molecules possess magnetic anisotropy energy which ma y not be strictly uniaxial. This, we believe, may be intimately connec ted with the mechanism causing the f-factor anomaly.