A reappraisal of the subunit molecular mass of chicken liver cytosol 5'-nucleotidase.

The subunit molecular mass of chicken liver cytosol 5'-nucleotidase was earlier reported to be 51 kDa upon sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (Naito, Y. and Tsushima, K. (1976) Biochim. Biophys. Acta 438, 159-168). By immunoblot analyses after SDS-gel electrophoresis, however, a fraction from the liver homogenized in the presence of leupeptin showed multiple bands with molecular masses around 57 kDa, and SDS-extracted proteins directly from the liver exhibited a single 70 kDa component. These results indicate that the 51 kDa peptide observed in the cytosol 5'-nucleotidase preparation might, in fact, be a proteolytic artifact.