Phosphorylation of two human neurochordins by mammalian casein kinase 1

Neurochordins are a family of immunologically interrelated high-M(r) neural tissue glycoproteins which includes four major molecular species and several minor ones. Incubation of the total preparation of immunoaffinity-isolated neurochordins with ATP and rabbit casein kinase 1 resulted in phosphorylation of two neurochordin polypeptides, A and B3. The maximum levels of modification were 7-8 and 2 mol of 32P incorporated per 1 mol of polypeptide, respectively. Phosphoamino acid analysis of the phosphorylated neurochordins showed that casein kinase 1 modified exclusively serine residues in both polypeptides. Casein kinase 2 was not effective in phosphorylating neurochordins in vitro.