The protein phosphatases involved in cellular regulation. 4. Classification of two homogeneous myosin light chain phosphatases from smooth muscle as protein phosphatase-2A1 and 2C, and a homogeneous protein phosphatase from reticulocytes active on protein synthesis initiation factor eIF-2 as protein phosphatase-2A2.
Two homogeneous protein phosphatases, termed 'smooth muscle phosphatase-I' and 'smooth muscle phosphatase-II', isolated from turkey gizzard as enzymes active against the 20-kDa light chain of smooth muscle myosin, and a third homogeneous protein phosphatase from rabbit reticulocytes, purified as an enzyme active against protein synthesis initiation factor eIF-2, were classified using the criteria defined by Ingebritsen and Cohen [Eur. J. Biochem. (1983) 132, 255-261]. All three enzymes were type-2 protein phosphatases based on their specificity for the alpha-subunit of phosphorylase kinase and insensitivity to inhibitor-1 and inhibitor-2. The substrate specificities of smooth muscle phosphatase-I and the eIF-2 phosphatase were similar to the catalytic subunit of protein phosphatase-2A. Smooth muscle phosphatase-I could be designated as protein phosphatase-2A1 and eIF-2 phosphatase as protein phosphatase-2A2 on the basis of their subunit compositions. The substrate specificity, dependence of activity on Mg2+ and subunit composition of smooth muscle phosphatase-II allowed its assignment as protein phosphatase-2C.
D000818:Animals; D015852:Eukaryotic Initiation Factor-2; D005895:Gizzard, Avian / Q000201:enzymology; D008099:Liver / Q000201:enzymology; D009124:Muscle Proteins / Q000378:metabolism*; D009130:Muscle, Smooth / Q000201:enzymology*; D009218:Myosins / Q000378:metabolism; D010448:Peptide Initiation Factors / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000145:classification / Q000302:isolation & purification / Q000502:physiology*; D054648:Protein Phosphatase 2; D011506:Proteins / Q000378:metabolism; D011817:Rabbits; D012156:Reticulocytes / Q000201:enzymology*; D014422:Turkeys
D015852:Eukaryotic Initiation Factor-2; D009124:Muscle Proteins; D010448:Peptide Initiation Factors; D011506:Proteins; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D009218:Myosins