Melanoblast/melanocyte early marker (MelEM) is a glutathione S-transferase subunit

We have biochemically characterized the antigen recognized by the melanoblast/melanocyte early marker (MelEM) monoclonal antibody (Mab) which labels early melanoblasts and melanocytes in the avian embryo [1]. While among the neural crest derivatives MelEM Mab is strictly specific for the melanocytic lineage, some endodermal derivatives such as hepatocytes react with this Mab. Since MelEM Mab immunoprecitates a protein of the same relative mass from both liver extracts and melanocytes, we immunopurified MelEM protein from liver extract of quail embryos at 10 days of incubation. The N-terminal sequence of this protein being blocked, we determined three internal peptide sequences. Our study reveals that the MelEM protein is an Alpha class subunit of glutathione S-transferase which is common to hepatocytes and to neural crest-derived pigment cells during their differentiation.