Journal ArticleDOI
The protein phosphatases involved in cellular regulation. 6. Measurement of type-1 and type-2 protein phosphatases in extracts of mammalian tissues; an assessment of their physiological roles.
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Protein phosphatase 2A was the major enzyme acting on L-pyruvate kinase, ATP-citrate lyase and acetyl-CoA carboxylase in rat liver, suggesting an important role in the regulation of glycolysis/gluconeogenesis and fatty acid synthesis and cholesterol synthesis.Abstract:
Methods were developed for quantifying protein phosphatases-1, 2A, 2B and 2C in cell extracts, and these procedures were exploited to determine their tissue and subcellular distributions. In addition, the contribution of each enzyme to the total protein phosphatase activity in skeletal muscle and liver extracts towards nine proteins involved in the control of glycogen metabolism, glycolysis/gluconeogenesis, fatty acid synthesis and cholesterol synthesis was assessed. Each protein phosphatase was present at significant concentrations in skeletal muscle, heart muscle, liver, brain and adipose tissue, although the relative amounts differed considerably. In skeletal muscle, protein phosphatase-1 was the major enzyme acting on phosphorylase, glycogen synthase and phosphorylase kinase (beta-subunit), and thus was the major protein phosphatase responsible for the inactivation of glycogenolysis and stimulation of glycogen synthesis. This idea was reinforced by the observation that 50% of the protein phosphatase-1 activity was associated with the protein-glycogen complex. In the liver, protein phosphatases-1, 2A and 2C each appear to play a role in the regulation of glycogen metabolism. Protein phosphatase-1 accounted for a significant fraction of the total potential activity towards phosphorylase and glycogen synthase, and was the major phosphorylase kinase (beta-subunit) phosphatase of this tissue. In addition, it was the only protein phosphatase present in the protein-glycogen complex. Protein phosphatase 2A was also a major phosphorylase phosphatase and glycogen synthase phosphatase in this tissue. Protein phosphatase 2C was a significant glycogen synthase phosphatase in the liver, but had negligible activity toward phosphorylase or phosphorylase kinase (beta-subunit). In the absence of Ca2+, protein phosphatase 2A was the major phosphorylase kinase (alpha-subunit) phosphatase and the only inhibitor-1 phosphatase, in skeletal muscle or liver. In the presence of Ca2+, protein phosphatase 2B accounted for most of the activity towards these substrates. Protein phosphatase 2A was the major enzyme acting on L-pyruvate kinase, ATP-citrate lyase and acetyl-CoA carboxylase in rat liver, suggesting an important role in the regulation of glycolysis/gluconeogenesis and fatty acid synthesis. Protein phosphatase 2C was the major enzyme acting on hydroxymethylglutaryl-CoA (HMG-CoA) reductase and HMG-CoA reductase kinase, suggesting an important role in the regulation of cholesterol synthesis. However, the observation that 20% of the protein phosphatase-1 in liver was associated with the microsomal fraction suggests that this enzyme may also be involved in regulating HMG-CoA reductase, which is tightly associated with microsomes. The activity of protein phosphatase-1 in dilute skeletal muscle and liver extracts was just as sensitive to inhibitor-1 and inhibitor-2 as the purified enzyme. In concentrated extracts, higher concentrations of the inhibitor proteins were required and the inhibition was time-dependent...read more
Citations
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Journal ArticleDOI
Cyanobacterial microcystin-LR is a potent and specific inhibitor of protein phosphatases 1 and 2A from both mammals and higher plants.
TL;DR: The cyclic heptapeptide, microcystin‐LR, inhibits protein phosphatases 1 (PP1) and 2A (PP2A) with K i, values below 0.1 nM, and this results are strikingly similar to those obtained with the tumour promoter okadaic acid.
Journal ArticleDOI
Calcineurin : form and function
Frank Rusnak,Pamela Mertz +1 more
TL;DR: This review provides a comprehensive examination of the biological roles of calcineurin and reviews aspects related to its structure and catalytic mechanism.
Journal ArticleDOI
Protein phosphatases: properties and role in cellular regulation
TL;DR: The properties, physiological roles, and mechanisms for regulating the four protein phosphatases are reviewed and their roles in controlling glycogen metabolism, glycolysis, gluconeogenesis, fatty acid synthesis, cholesterol synthesis, and protein synthesis are reviewed.
Journal ArticleDOI
Biopsy-derived adult human brain tau is phosphorylated at many of the same sites as Alzheimer's disease paired helical filament tau
Eriko S. Matsuo,Ryong Woon Shin,Melvin L. Billingsley,Andre Van deVoorde,Michael J. O'Connor,John Q. Trojanowski,Virginia M.-Y. Lee +6 more
TL;DR: Examination of human adult tau from brain biopsies demonstrated that biopsy-derived tau is phosphorylated at most sites thought to be abnormally phosphorylate tau, suggesting that the down-regulation of phosphatases in the AD brain could lead to the generation of maximallyosphorylated PHF-tau that does not bind microtubules and aggregates as PHFs in neurofibrillary tangles and dystrophic neurites.
Journal ArticleDOI
The molecular mechanism by which insulin stimulates glycogen synthesis in mammalian skeletal muscle
TL;DR: An insulin-stimulated protein kinase is shown to activate the type-1 protein phosphatase that controls glycogen metabolism, by phosphorylating its regulatory subunit at a specific serine.
References
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Journal ArticleDOI
The role of protein phosphorylation in neural and hormonal control of cellular activity
TL;DR: There is an integrated network of regulatory pathways, mediated by phosphorylation–dephosphorylation, that allows diverse cellular events to be coordinated by neural and hormonal stimuli, and the evidence that supports this concept is reviewed.
Journal ArticleDOI
Separation and Characterization of Two Phosphorylase Phosphatase Inhibitors from Rabbit Skeletal Muscle
TL;DR: Two heat-stable and trypsin-labile inhibitors of phosphorylase phosphatase, designated inhibitor-1 and inhibitor-2, were partially purified from extracts of rabbit skeletal muscle by heating and coloumn chromatography using DEAE-dellulose and Bio-gel P-60.
Journal ArticleDOI
Multimolecular forms of pyruvate kinase from rat and other mammalian tissues. I. Electrophoretic studies.
Kiichi Imamura,Takehiko Tanaka +1 more
Journal ArticleDOI
Control of phosphorylase activity in a muscle glycogen particle. I. Isolation and characterization of the protein-glycogen complex.
TL;DR: All three preparations were essentially identical in terms of their physical, chemical, and enzymatic characteristics strongly suggesting that the protein-glycogen complex represents a structural and functional unit of the cell rather than artifacts resulting from a given isolation procedure.
Book ChapterDOI
The role of cyclic-AMP-dependent protein kinase in the regulation of glycogen metabolism in mammalian skeletal muscle.
TL;DR: The role of cyclic-AMP-dependent protein kinase in the regulation of glycogen metabolism in mammalian skeletal muscle is discussed, which determines the time at which dephosphorylation of the β subunit and inactivation of the enzyme can become rapid through phosphorylations of the α subunit.