Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:3.1.3.16 (calcineurin)
17,112 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The prominent protein phosphatases involved in liver glycogen metabolism are the AMD (ATP, Mg-dependent, type-1) and PCS (polycation-stimulated, type-2A) phosphatases. The glycogen synthase phosphatase activity, measured from the rate of activation of liver glycogen synthase, is virtually accounted for by AMD phosphatases; the bulk of the activity belongs to the glycogen-bound protein phosphatase G and a small part is present in the cytosol. The major part of the phosphorylase phosphatase activity present in the post-mitochondrial supernatant is shared by protein phosphatase G and cytosolic enzymes, and a minor part belongs to a microsomal AMD phosphatase. In the liver cytosol, the phosphorylase phosphatase activity is about equally distributed between AMD and PCS phosphatases. Studies in vivo as well as on isolated, perfused livers have shown that glucagon (which raises the level of cyclic AMP) as well as vasopressin (which increases the cytosolic Ca2+ concentration) decrease the phosphorylase phosphatase activity in liver extract or cytosol (filtered through Sephadex G-25) by about 25% within a few minutes. These effects were not additive, and the activity of glycogen synthase phosphatase was not affected. Conversely, insulin as well as glucose increased both phosphatase activities by about 25%, and these effects were additive. Vanadate mimicked the effect of insulin on the perfused liver. All the activity changes were only observed when the assays were performed at high tissue concentration. Upon subcellular fractionation all the effects were well expressed in the cytosol, but not in the particulate fraction (glycogen and microsomes). However, quantitatively the hormonal responses were largely lost during the fractionation procedure; they could be restored by recombination of the liver cytosol from a hormone-treated rat with the particulate fraction from either a treated or an untreated animal. It appears that the effects of glucagon, insulin and glucose are mediated by cytosolic, transferable effectors of the Vmax of protein phosphatases. These effectors are eluted in the void volume of a Sephadex G-25 column. Rats of the gsd/gsd strain, which have a genetic deficiency of hepatic phosphorylase kinase, responded to an injection of insulin plus glucose with a normal increase in the cytosolic phosphorylase phosphatase activity. In contrast, they failed to respond to glucagon as well as vasopressin. A transient 80% inhibition of the phosphorylase phosphatase activity could be induced in vitro in a concentrate liver cytosol from Wistar rats upon addition of MgATP.(ABSTRACT TRUNCATED AT 400 WORDS)
...
PMID:Short-term hormonal control of protein phosphatases involved in hepatic glycogen metabolism. 216 98

1. Glycogen synthase from rabbit skeletal muscle was phosphorylated by phosphorylase kinase to yield synthase b2. 2. Dephosphorylation and activation of synthase b2 by the catalytic subunits of protein phosphatase-1 (PP-1c) and protein phosphatase-2A (PP-2Ac) was studied. The apparent Km of PP-1c and PP-2Ac were 3.3 microM and 6.2 microM, respectively. The apparent Vmax of PP-1c was about two times larger than that of PP-2Ac. 3. Ligands with phosphate moiety (AMP, glucose-6-P at high concentration) caused an inhibition in dephosphorylation by both phosphatases. Spermine inhibited the dephosphorylation by PP-1c and stimulated the action of PP-2Ac. Therefore it can be employed to distinguish the phosphatases using synthase b2 as substrate.
...
PMID:Activation/dephosphorylation of muscle glycogen synthase phosphorylated by phosphorylase kinase. 250 70

Ribosomal protein S6 is the principal phosphoprotein of the eucaryotic ribosome that becomes multiply phosphorylated on serine residues in response to a wide variety of mitogenic stimuli. In this paper the principal protein phosphatases able to dephosphorylate S6 were characterized in Xenopus laevis ovary and eggs. Two enzymes termed peak I and peak II were found to account for most S6 phosphatase activity in both oocytes and eggs. The peak I enzyme had an apparent Mr of 200,000 on gel filtration, dephosphorylated the beta subunit of phosphorylase kinase and phosphorylase a, and was inhibited by inhibitor 1 and inhibitor 2, suggesting it was similar to protein phosphatase 1. The peak II enzyme was purified over 12,000-fold and had an apparent Mr = 55,000 on glycerol gradient centrifugation. This phosphatase could dephosphorylate all sites in S6 but was unable to dephosphorylate phosphorylase a or phosphorylase kinase. However, it was inhibited by nanomolar concentrations of inhibitor 1 and inhibitor 2. These results indicate the peak II enzyme represents a new class of highly specific protein phosphatase and suggest that inhibition of dephosphorylation in cellular extracts by inhibitor 1 and inhibitor 2 is not a sufficient criterion for implicating protein phosphatase 1 in a cellular process.
...
PMID:Purification and characterization of a novel protein phosphatase highly specific for ribosomal protein S6. 253 37

Ca2+-calmodulin-dependent protein phosphatase activity is found in cytoskeletons of Y-1 mouse adrenal and bovine fasciculata cells. The activity is inhibited by three inhibitors of calmodulin (trifluoperazine, W-7 and pimozide) with EC50 in the low micromolar range. Protein phosphatase activity is inhibited by vanadate, fluoride, Zn2+ and pyrophosphate, stimulated by Mn2+ and found to be tightly bound to the cytoskeleton. Substrates for endogenous phosphatase activity were defined by one- and two-dimensional polyacrylamide gels. Phosphatase activity was seen with proteins that are substrates for both cyclic AMP-dependent and cyclic AMP-independent kinase enzymes. One specific Ca2+-calmodulin-dependent phosphatase, namely calcineurin, was purified to near homogeneity from cytoskeletons of Y-1 cells. The enzyme was found to be a heterodimer (MW 61,000 and 16,000) and the smaller subunit was shown to cross-react with antibodies raised against calcineurin from bovine brain. The purified enzyme catalyzes dephosphorylation of proteins (phosphorylase kinase and casein), phosphoamino acids (tyr greater than thre greater than ser) and a synthetic substrate (p-nitrophenyl phosphate). In addition, a new application of membrane transfer was devised by which the purified enzyme was incubated with a Western blot of cytoskeleton following incubation with [32P]ATP. This method defined four specific substrates of the enzyme (MW 150,000, 55,000, 35,000 and 30,000). Anti-calcineurin revealed that only a single Ca2+-calmodulin-dependent phosphatase is found in adrenal cell cytoskeleton.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Isolation and characterisation of calcineurin from adrenal cell cytoskeleton: identification of substrates for Ca2+-calmodulin-dependent phosphatase activity. 254 40

Infection of Escherichia coli with phage lambda gt10 resulted in the appearance of a protein phosphatase with activity towards 32P-labelled casein. Activity reached a maximum near the point of cell lysis and declined thereafter. The phosphatase was stimulated 30-fold by Mn2+, while Mg2+ and Ca2+ were much less effective. Activity was unaffected by inhibitors 1 and 2, okadaic acid, calmodulin and trifluoperazine, distinguishing it from the major serine/threonine-specific protein phosphatases of eukaryotic cells. The lambda phosphatase was also capable of dephosphorylating other substrates in the presence of Mn2+, although activity towards 32P-labelled phosphorylase was 10-fold lower, and activity towards phosphorylase kinase and glycogen synthase 25 50-fold lower than with casein. No casein phosphatase activity was present in either uninfected cells, or in E. coli infected with phage lambda gt11. Since lambda gt11 lacks part of the open reading frame (orf) 221, previously shown to encode a protein with sequence similarity to protein phosphatase-1 and protein phosphatase-2A of mammalian cells [Cohen, Collins, Coulson, Berndt & da Cruz e Silva (1988) Gene 69, 131-134], the results indicate that ORF221 is the protein phosphatase detected in cells infected with lambda gt10. Comparison of the sequence of ORF221 with other mammalian protein phosphatases defines three highly conserved regions which are likely to be essential for function. The first of these is deleted in lambda gt11.
...
PMID:Discovery of a protein phosphatase activity encoded in the genome of bacteriophage lambda. Probable identity with open reading frame 221. 254 89

Protein phosphatases assayed with phosphorylase alpha are present in the soluble and particulate fractions of rat thymocytes. Phosphorylase phosphatase activity in the cytosol fraction was resolved by heparin-Sepharose chromatography into type-1 and type-2A enzymes. Similarities between thymocyte and muscle or liver protein phosphatase-1 included preferential dephosphorylation of the beta subunit of phosphorylase kinase, inhibition by inhibitor-2 and retention by heparin-Sepharose. Similarities between thymocyte and muscle or liver protein phosphatase-2A included specificity for the alpha subunit of phosphorylase kinase, insensitivity to the action of inhibitor-2, lack of retention by heparin-Sepharose and stimulation by polycationic macromolecules such as polybrene, protamine and histone H1. Protein phosphatase-1 from the cytosol fraction of thymocytes had an apparent molecular mass of 120 kDa as determined by gel filtration. The phosphatase-2A separated from the cytosol of thymocytes may correspond to phosphatase-2A0, since it was completely inactive (latent) in the absence of polycation and had activity only in the presence of polycations. The apparent molecular mass of phosphatase-2A0 from thymocytes was 240 kDa as determined by gel filtration. The catalytic subunit of thymocyte type-1 protein phosphatase was purified with heparin-Sepharose chromatography followed by gel filtration and fast protein liquid chromatography on Mono Q column. The purified type-1 catalytic subunit exhibited a specific activity of 8.2 U/mg and consisted of a single protein of 35 kDa as judged by SDS-gel electrophoresis. The catalytic subunit of type-2A phosphatase from thymocytes appearing in the heparin-Sepharose flow-through fraction was further purified on protamine-Sepharose, followed by gel filtration. The specific activity of the type-2A catalytic subunit was 2.1 U/mg and consisted of a major protein of 34.5 kDa, as revealed by SDS-gel electrophoresis.
...
PMID:Purification and partial characterization of protein phosphatases from rat thymus. 255 7

The glycogen-associated form of protein phosphatase-1 (PP-1G) is a heterodimer comprising a 37-kDa catalytic (C) subunit and a 161-kDa glycogen-binding (G) subunit, the latter being phosphorylated by cAMP-dependent protein kinase at two serine residues (site 1 and site 2). Here the amino acid sequence surrounding site 2 has been determined and this phosphoserine shown to lie 19 residues C-terminal to site 1 in the primary structure. The sequence in this region is: (sequence; see text) At physiological ionic strength, phosphorylation of glycogen-bound PP-1G was found to release all the phosphatase activity from glycogen. The released activity was free C subunit, and not PP-1G, while the phospho-G subunit remained bound to glycogen. Dissociation reflected a greater than or equal to 4000-fold decrease in affinity of C subunit for G subunit and was readily reversed by dephosphorylation. Phosphorylation and dephosphorylation of site 2 was rate-limiting for dissociation and reassociation of C subunit. Release of C subunit was also induced by the binding of anti-site-1 Fab fragments to glycogen-bound PP-1G. At near physiological ionic strength, PP-1G and glycogen concentration, site 2 was autodephosphorylated by PP-1G with a t0.5 of 2.6 min at 30 degrees C, approximately 100-fold slower than the t0.5 for dephosphorylation of glycogen phosphorylase under the same conditions. Site 2 was a good substrate for all three type-2 phosphatases (2A, 2B and 2C) with t0.5 values less than those toward the alpha subunit of phosphorylase kinase. At the levels present in skeletal muscle, the type-2A and type-2B phosphatases are potentially capable of dephosphorylating site 2 in vivo within seconds. Site 1 was at least 10-fold less effective than site 2 as a substrate for all four phosphatases. In conjunction with information presented in the following paper in this issue of this journal, the results substantiate the hypothesis that PP-1 activity towards the glycogen-metabolising enzymes is regulated in vivo by reversible phosphorylation of a targetting subunit (G) that directs the C subunit to glycogen--protein particles. The efficient dephosphorylation of site 2 by the Ca2+/calmodulin-stimulated protein phosphatase (2B) provides a potential mechanism for regulating PP-1 activity in response to Ca2+, and represents an example of a protein phosphatase cascade.
...
PMID:Regulation of protein phosphatase-1G from rabbit skeletal muscle. 1. Phosphorylation by cAMP-dependent protein kinase at site 2 releases catalytic subunit from the glycogen-bound holoenzyme. 255 13

Two types of protein phosphatases were identified in carefully prepared bovine rod outer segments (ROS). Extraction of the ROS with a medium-salt buffer solubilized protein phosphatase activity that was mainly type 2A, since it was active toward phosphorylase a in the absence of divalent cations, was not retained by heparin-Sepharose, dephosphorylated the alpha-subunit of phosphorylase kinase faster that the beta-subunit, and was unaffected by inhibitor 2. Further extraction of the resulting membranes with a high-salt buffer solubilized additional phosphatase activity which was predominantly type 1, since it was retained by heparin-Sepharose and was blocked by inhibitor 2. The molecular mass of the type 2A phosphatase estimated by gel permeation chromatography on Superose 12 was 100 kDa, suggesting it may be the 2A2 form. Only the ROS type 2A phosphatase dephosphorylated opsin and rhodopsin efficiently. Concordant with this finding, the purified catalytic subunit of protein phosphatase 2A from rabbit skeletal muscle dephosphorylated opsin efficiently, while the type 1 catalytic subunit isolated from this tissue was inactive. Together, the results suggest that the ROS type 2A protein phosphatase plays an important role in regenerating rhodopsin from the various phosphorylated species in vivo. The activity of the enzyme per retina (approximately 85 pmol of Pi released/min) is comparable to that of rhodopsin kinase (100 pmol of phosphate transferred/min).
...
PMID:Interplay of phosphorylation and dephosphorylation in vision: protein phosphatases of bovine rod outer segments. 255 19

1. Hearts of diabetic rats gradually accumulate glycogen, although the activities of glycogen synthase and glycogen phosphorylase are altered in favor of a depletion of glycogen. 2. Phosphorylase in diabetic hearts has been reported to be even more activated in response to adrenaline than controls. 3. The situation is further complicated by the fact that in rat heart two isoenzymes of phosphorylase are present. Therefore we have studied the properties of phosphorylases purified from diabetic rat heart in more detail. 4. This investigation revealed that compared to controls: (A) the amount of enzyme protein which could be isolated from diabetic animals is drastically lower; (B) the affinities towards glycogen and inorganic phosphate are decreased; (C) the activation by phosphorylase kinase is delayed; and (D) the inactivation by protein phosphatase-1 is accelerated. 5. We conclude that all of the reported changes in diabetes might contribute to a phosphorylase system less able to catalyze glycogen breakdown effectively.
...
PMID:Activation and inactivation of glycogen phosphorylase isoenzymes purified from diabetic rat heart. 274 7

To gain more insight into the nature of the substrate specificity of protein phosphatases, four forms of glycogen synthase D were used as substrates for previously characterized protein phosphatases, IA, IB, and II, from rat liver cytosol. The phosphatase activity was measured as the conversion of glycogen synthase D to synthase I. While glycogen synthase isolated from rat liver as the D-form was activated mainly by phosphatase IA, rabbit skeletal muscle glycogen synthase previously phosphorylated in vitro by cyclic AMP-dependent protein kinase or phosphorylase kinase was activated efficiently by phosphatases IA, IB, and II. Glycogen synthase isolated from rabbit skeletal muscle as the D-form, however, was a poor substrate for all three phosphatases. These results suggest that the phosphorylation state as well as the primary structure of synthase D markedly affects the rate of its activation by individual protein phosphatases. A protein phosphatase released from rat liver particulate glycogen, on the other hand, activated all forms of synthase D used here readily and at about the same rate.
...
PMID:Activation of rat liver and rabbit skeletal muscle glycogen synthases by rat liver cytosolic protein phosphatases. 282 Sep 52


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---