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Keywords:

Amino Acid Sequence, Animals, Carrier Proteins, Cattle, Dopamine and cAMP-Regulated Phosphoprotein 32, Enzyme Activation, Intracellular Signaling Peptides and Proteins, Kinetics, Molecular Sequence Data, Nerve Tissue Proteins, Phosphoprotein Phosphatase, Phosphoproteins, Phosphorylation, Protein Kinases, Proteins, Rabbits, Research Support, Non-U.S. Gov't, Science & Technology, Life Sciences & Biomedicine, Biochemistry & Molecular Biology, CYCLIC-AMP, CATALYTIC SUBUNIT, PHOSPHORYLATION, DEPHOSPHORYLATION, PHOSPHOPROTEIN, SUBSTRATE, PEPTIDES, DARPP-32, TYPE-1, MUSCLE, Phosphoprotein Phosphatases, Protein Phosphatase 1, Protein Phosphatase 2, 03 Chemical Sciences, 06 Biological Sciences, 11 Medical and Health Sciences, 31 Biological sciences, 32 Biomedical and clinical sciences, 34 Chemical sciences

Abstract:

We have recently purified two potent and specific inhibitory polypeptides of protein phosphatase-1 from the particulate fraction of bovine thymus nuclei (Beullens, M., Van Eynde, A., Stalmans, W., and Bollen, M. (1992) J. Biol. Chem. 267, 16538-16544). Here it is reported that these inhibitors, termed NIPP-1a (18 kDa) and NIPP-1b (16 kDa), are excellent substrates (Km = 0.1 microM) for phosphorylation by protein kinase A on both Ser and Thr residues. Phosphorylation was temporally closely related with an activation of NIPP-1. Maximal phosphorylation by protein kinase A (1.5 mol of phosphate/mol of NIPP-1) caused an 8-fold increase in the concentration of NIPP-1 required for half-complete inhibition of the catalytic subunit of protein phosphatase-1, irrespective of the concentration of the phosphatase. Phosphorylation decreased the binding of NIPP-1 to immobilized protein phosphatase-1. NIPP-1 could be efficiently and completely reactivated by incubation with the catalytic subunit of protein phosphatase-2A. The type-1 catalytic subunit was much less effective, however, even when present in a molar excess to NIPP-1. Chromatography of a salt extract of the particulate nuclear fraction of Mono Q revealed three species of PP-1. One of these species, termed PP-1N alpha, contained NIPP-1 as a subunit and could be activated 6-fold by incubation with protein kinase A under phosphorylating conditions. This activation of PP-1N alpha is opposite to the known inhibition of cytoplasmic species of protein phosphatase-1 by protein kinase A.