Short communication: Bovine alpha-casein is a ferritin-binding protein and inhibitory factor of milk ferritin immunoassay.

Commercial bovine milk alpha-casein, but not beta- and kappa-caseins, bound to bovine spleen ferritin, as determined by an immunoassay for ferritin. In contrast, alpha-casein did not bind to apoferritin. The binding of alpha-casein to bovine spleen ferritin was strongly inhibited by increasing ionic strength by the addition of 0.5 M (NH(4))(2)SO(4). The addition of alpha-casein to a known amount of bovine spleen ferritin resulted in significantly lower recovery (78-80%) of added ferritin, although beta- and kappa-caseins showed little inhibitory effect in the ferritin immunoassay. These results indicate that bovine alpha-casein is a specific ferritin-binding protein that may inhibit milk ferritin immunoassay.