Expression and Characterization of Rat Protein Phosphatases-1α, -1γ1, -1γ2, and -1δ

Four distinct cDNAs for rat protein phosphatase-1 have been isolated from rat tissues (Sasaki et al., Jpn. J. Cancer Res. 81, 1272-1280, 1990). These cDNAs encode proteins of highly similar sequence, the major differences being located at their N and C termini. In order to demonstrate that these cDNAs encode functional proteins and to investigate their enzymatic properties, it would be desirable to obtain purified preparations of these proteins. Using a system that was developed for the expression of rabbit muscle protein phosphatase-1 (Zhang et al., J. Biol. Chem. 267, 1484-1490, 1992) we have expressed these isoforms in Escherichia coli. The four recombinant isoforms were purified to near homogeneity and their properties were examined in terms of substrate specificity and sensitivity to okadaic acid and inhibitor-2.