High levels of ferritin and its iron in fetal bovine serum.

In 13 lots of the commercial fetal bovine sera, the ferritin levels ranged between 0.8 and 6.0 micrograms/ml. The serum ferritin iron concentration as measured by a quantitative immunoprecipitation technique ranged from 0.16 to 0.96 microgram/ml, and the iron content of ferritin was about 20% regardless of its protein concentration in sera. The percentage of ferritin iron to total serum iron ranged from 8.8 to 28.5%, and correlated significantly with ferritin concentration (r = 0.9368, P < 0.001). No significant proportion of the ferritin in fetal serum bound to concanavalin A. Immunoblotting showed that the molecular weights of L(iver)- and H(eart)-type subunits of fetal serum ferritin were identical to those of L and H subunits of adult bovine spleen ferritin (L:21kDa, H:18kDa), respectively, and that the L subunit predominated in the serum protein. Serum transferrin level was relatively constant (1.8-2.2 mg/ml), whereas transferrin saturation varied from 54.8 to 91.7%. There was a significant correlation between serum ferritin concentration and transferrin saturation (r = 0.8864, P < 0.001). These findings demonstrate that the bovine fetuses have the elevated iron stores.