[Biosynthesis of ceruloplasmin in various rat organs]

Ceruloplasmin (CP) biosynthesis in various organs of the rat was studied. It was found that the translation products of postmitochondrial extracts of various organs of the rat contain immunoreactive polypeptides of CP. In respect of proteolytic fragments formed during the digestion with staphylococcal protease V8, these polypeptides do not differ from one another. At the same time, in Golgi vesicles of the kidney, brain and liver the mature molecular forms of CP differ not only by their molecular properties, but also by the number of CP isoforms. For example, the organs which do not secrete CP, contain only one isoform of CP. The secreted form of CP was found to be tissue-nonspecific. The third molecular form of CP found in the liver has no counterparts in the other organs. Immunochemical analysis of mature forms of CP isolated from liver Golgi vesicles provided additional evidence in favour of molecular heterogeneity of CP secreted by the liver. The mechanism of production of multiple molecular forms of CP and their roles in copper metabolism are postulated.