Topography, purification and characterization of thyroidal 5'-nucleotidase.

1. Subcellular studies of bovine thyroid indicate that 5'-nucleotidase is predominantly associated with plasma membranes, although a considerable part of this ectoenzyme is also found internalized. 2. The enzyme displaying the features of a glycoprotein has been purified 1400 times by detergent solubilization and two subsequent affinity chromatographic steps. 3. Thyroidal 5'-nucleotidase can be classified as an unspecific metallo-dependent 5'-ribonucleotide phosphohydrolase. The native enzyme exists as a dimer (MW 150 kDalton), composed of two similar or identical subunits.