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Electron paramagnetic resonance (EPR) spectra have been obtained on iron and copper protein complexes of human blood serum transferrin, human lactotransferrin, and conalbumins obtained from chicken, turkey, and Japanese quail egg whites. The EPR results indicate that Fe+3 and Cu+2 both bind to similar sites and that there is no magnetic interaction between the bound metal atoms. No difference between the sites binding the first and second moles of metal was detected by EPR. It is proposed that Cu+2 is bound to two tyrosyl oxygen atoms and two nitrogen atoms of the protein with square planar coordination, and that Fe+S is octahedrally coordinated to three tyrosyl oxygen atoms, two nitrogen atoms, and one bicarbonate ion.

Hematopoietic cells have been demonstrated to survive in many nonhematopoietic tissues after transplantation. Apparent "bone marrow-derived" cerebellar Purkinje cells in fact result from fusion events and it has been suggested that fusion may be a natural physiological phenomenon to rescue dysfunctioning cells. Here, we show that fusion of transplanted bone marrow cells with resident Purkinje cells is age-dependent and is strongly enhanced when Purkinje cells are damaged by high-dose irradiation. In addition, Purkinje heterokaryons occur in increased frequencies in the cerebellum of normal, unperturbed, aged mice compared to young animals. Our data suggest that age- and/or irradiation-induced dysfunctioning of Purkinje cells in the cerebellum is required for cell fusion.

A number of organic compounds containing sulfur or selenium are known to be useful as antioxidants or radio-protective agents because of their reactivity with free radicals. We have studied the electron paramagnetic resonance (EPR) of some aliphatic and aromatic sulfide and disulfide compounds and their selenium analogs uv-irradiated at λ=2537 Å in order to characterize and compare the free radicals produced. The irradiation and the EPR measurements were carried out at liquid nitrogen temperature. The EPR spectra obtained for these compounds fall into four categories characteristic of the four types of radical species found—alkyl radicals, benzyl-type radicals, sulfur radicals, and selenium radicals. The selenium radical, which has not been previously observed, exhibits an asymmetric spectrum having an axially symmetric g factor, with g⊥=2.08 and g∥=2.12.