PURIFICATION OF A NOVEL GLYCOSYLATED FERRITIN FROM HORSE HEART

We have previously shown that mRNA coding for ferritin L subunit is pr esent on both cytosolic ribosomes and endoplasmic reticulum-bound ribo somes in rat heart tissue [Campbell et al. (1989) Arch Biochem Biophys 273:89-981; from this we infer that heart tissue is capable of making a secreted ferritin. We now report the purification from horse heart, of a ferritin that specifically binds to Conconavalin A-Sepharose and is immunologically cross-reactive with antibodies raised against both horse cellular ferritin and horse serum ferritin. Where cellular ferr itin is 10 nm in diameter and contains primarily 21-kDa subunits (as d etermined by gel exclusion chromatography and electron microscopy), th e glycosylated heart ferritin is smaller with diameters of 3-5 nm. Ant isera raised against serum ferritin cross-reacted with the glycosylate d heart ferritin did but did not show significant cross-reactivity wit h cellular ferritin thus indicating that serum ferritin and glycosylat ed heart ferritin have antigenic determinants which may not be present on cellular ferritin. The glycosylated ferritin also differs from cel lular ferritin in subunit composition, with subunits of 66, 60.5, 53.5 , 43.5, and 29.5 kDa, as shown by SDS-PAGE and Western blot analysis. Interestingly, ferritin purified from horse serum contains subunits of similar size. (C) 1993 Wiley-Liss, Inc.