Analysis of the Isoforms of Protein Phosphatase 1 (PP1) Isoforms with Polyclonal Peptide Antibodies

Abstract

Various isoforms of the catalytic subunit of Protein Phosphatase-1 (Ser/Thr phosphatase of type-1, PP1) were discovered by cDNA cloning (1). PP1α, PP1γ1 and PP1δ (also called β) are found in virtually all mammalian cells, whereas PP1γ2 is testis-specific (2,3). Although PP1α, PP1γ1, and PP1δ are products of different genes, they are about 90% identical (2) and migrate as a single protein band on SDS-electrophoresis. For instance, the 37 kDa PP1 purified from rabbit muscle is a mixture of the three isoforms (4,5). The only sequence differences among the isoforms are in the C-termini (2). Consequently, only antibodies to peptides derived from these regions are isoform-specific (5,6). Based on the involvement of PP1 in many different regulatory pathways, differential subcellular localizations for the isoforms may be envisaged, These studies require isoform-specific antibodies, such as those produced and purified using the procedures described herein. The authors also show how the antibodies can be used to distinguish the PP1 isoforms in immunoblot, immunoprecipitate, two-dimensional electrophoresis, and immunofluorescence.