Sequence homologies between type 1 and type 2A protein phosphatases

The Mr = 33,000 catalytic fragment of rabbit skeletal muscle type 1 protein phosphatase was digested with trypsin after reduction and alkylation. The resulting peptides were isolated, subjected to automated Edman degradation, and their sequences compared to the deduced peptide sequence of the bovine type 2A protein phosphatase cDNA. Of 10 tryptic peptides from the type 1 phosphatase that were sequenced, nine showed a high degree of homology with the type 2A phosphatase. This provides the first direct sequence comparison suggesting that the type 1 and type 2 protein phosphatases, distinguished functionally by their substrate specificities and sensitivity to inhibitors, make up part of a family of closely related gene products with similar structures.