Ea4 peptide of rainbow trout pro-IGF-I has been shown to exert anti-cancer activities in human cancer cell lines. Kou and Chen (2003) have shown that the trout Ea-4 peptide could bind specifically with a binding component on the membrane of neuroblastoma cells (SK-NF-1). In order to characterize this binding component, a radio-labeled ligand with high specific activity will be required. In this study, effort was made to label trout Ea4-peptide by phosphorylation by protein kinase A (PKA) with radioactive ATP. Recombinant PKA4 peptide was prepared by adding 5 amino acid residues to the...