Purification of terminal deoxynucleotidyl transferase from pig thymus: identification of 42,000 and 57,000 dalton species.

Terminal deoxynucleotidyl transferase [EC 2.7.7.31] has been purified 4,365-fold from pig thymus. It was further separated into two molecular forms of 57,000 and 45,000 daltons by Sephadex G-100 gel-filtration. The former sedimented at 4.2S through a sucrose gradient, while the latter sedimented at 3.6S. By sodium dodecyl sulfate-polyacrylamide gel-electrophoresis, their molecular weights were estimated at 57,000 and 42,000 daltons, respectively. Thus, the large and small pig terminal deoxynucleotidyl transferases both consist of a single polypeptide of 57,000 and 42,000 daltons and have no subunit structure. These two forms were indistinguishable in antigenicity as examined by a neutralization assay with an anti-calf terminal deoxynucleotidyl transferase antibody. The enzymatic properties of 42,000-dalton terminal deoxynucleotidyl transferase from pig thymus were very similar to those of the calf enzyme, which has a two-subunit structure.