STUDIES ON THE INTERACTION BETWEEN FERRITIN AND CERULOPLASMIN

We showed previously that ceruloplasmin associates with the H chain of rat liver ferritin during iron loading into ferritin such that the ir on oxidized by ceruloplasmin was deposited into ferritin [S.-H. Juan c t al. (1997) Arch. Biochem. Biophys. 341, 280-286]. Three synthetic de capeptides derived from domains 2, 4, and 6 of ceruloplasmin, referred to CP-2, CP-4, and CP-6, were utilized to identify a possible binding site on ceruloplasmin for ferritin, Two of the peptides, CP-4 and CP- 6, were found to inhibit iron loading into the recombinant ferritin H chain homopolymer (rH-Ft) by ceruloplasmin. The extent of inhibition o f iron loading into ferritin by ceruloplasmin by CP-6, but not CP-4, v aried with pH, whereas the inhibitory effect remained constant in incr easing concentrations of NaCl. The addition of rH-Ft quenched the fluo rescence emission of CP-4 and CP-6, but not CP-2. The quenching of flu orescence was used to estimate dissociation constants for the peptides . Iron loading into ferritin in Hepes buffer was not affected in the p resence of these peptides. In addition, synthetic peptides correspondi ng to the BC loop of ferritin H and L chains were utilized to localize an interaction site on ferritin for ceruloplasmin. The BC loop of H c hain but not L chain of ferritin stimulated the ferroxidase activity o f ceruloplasmin. Only the BC loop of ferritin H chain decreased the am ount of iron loading into ferritin by ceruloplasmin. (C) 1998 Academic Press.