Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.3.16 (calcineurin)
 17,112 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A simple and reproducible radioimmunoassay of the epidermal growth factor (EGF) receptor which uses 32P-labeled EGF receptor and anti-receptor monoclonal antibodies is reported. In vitro phosphorylation of A431 cell membranes with [gamma-32P]ATP in the presence of 20% dimethyl sulfoxide (which stimulates autophosphorylation of the EGF receptor) and 10 microM Na3VO4 (a potent inhibitor of phosphotyrosyl protein phosphatase) provides radiolabeled EGF receptor for radioimmunoassay without further purification. The most selective phosphorylation of the EGF receptor is achieved at ATP concentrations of 0.1-0.2 microM, which corresponds to the reported Km value for the autophosphorylation reaction of the EGF receptor (W. Weber, P.J. Bertics, and G.N. Gill, 1984, J. Biol. Chem. 259, 14631-14939). The incorporation of 32P into EGF receptors increases in proportion to the increase of ATP concentration up to 6 mol of labeled phosphate at 2.0 microM ATP. The label is entirely on tyrosine residues. The cell membranes can be stored at -70 degrees C for 3 months without loss of immunoreactivity and autophosphorylating activity. Standard curves for the radioimmunoassay were constructed employing either A431 cell membranes or whole cell homogenates containing a known amount of EGF receptor. The assay can detect 7 X 10(10) EGF receptor molecules or 20 ng of the receptor protein, and can quantitatively distinguish the difference in EGF receptor numbers between A431 cells and 29E2 and KB cells with 10-fold and 15-fold fewer receptors than A431 cells, respectively. 29E2 cells and KB cells express twofold more immunoreactive EGF receptors than EGF-binding sites. In contrast, A431 cells possess the same number of immunoreactive sites and receptor sites for EGF binding. To assess total EGF receptor expression, it is necessary to use a method which detects EGF receptors regardless of their intrinsic kinase activity, or capacity to bind EGF. This radioimmunoassay detects immunoreactive receptor molecules, even those which do not bind EGF.
Anal Biochem 1985 Sep
PMID:A direct radioimmunoassay for human epidermal growth factor receptor using 32P-autophosphorylated receptor. 300 Feb 17

The activating factor FA of the ATP.Mg-dependent protein phosphatase FcM was purified to near homogeneity from pig brain by a procedure involving chromatography on phosphocellulose, phosvitin-Sepharose 4B, and Blue Sepharose CL-6B. A specific myelin basic protein (MBP) kinase was found to co-purify with FA in a constant ratio throughout purification. It also proved impossible to separate the two activities on nondenaturing gel electrophoresis and 5-20% sucrose density gradient ultracentrifugation. Kinetic study indicated that MBP, presumably a substrate for FA, could compete with FcM for FA and thereby prevent the FA-mediated activation of the FcM activity. All the results taken together demonstrate that MBP kinase and FA are localized on the same protein. This, together with the data that FA, by activating the ATP.Mg-dependent phosphatase, promotes the dephosphorylation of [32P]MBP, phosphorylated by FA itself, suggests the evidence for a protein bearing two opposing activities involved in the regulation of brain functions. Moreover, since FA is tightly associated with the purified brain myelin membrane, the results further support the notion that FA may well be an endogenous protein kinase responsible for the cyclic phosphorylation-dephosphorylation of the central nervous system myelin.
J Biol Chem 1986 Sep 05
PMID:Identification of the ATP.Mg-dependent protein phosphatase activator (FA) as a myelin basic protein kinase in the brain. 301 47

The two recently discovered forms of protein phosphatase 2C, termed 2C1 and 2C2, were digested with CNBr or trypsin, and several peptides corresponding to two regions of the protein were sequenced. These studies revealed close homology between the two enzymes with 49 identities over the 62 residues that could be compared directly. The results establish that protein phosphatases 2C1 and 2C2 are the products of different genes. The C-terminus of protein phosphatase 2C2 has also been identified.
Biochim Biophys Acta 1987 Sep 14
PMID:Primary structure analysis proves that protein phosphatases 2C1 and 2C2 are isozymes. 304 Jan 25

The nature of protein phosphatases of the guinea-pig parotid gland was investigated. The protein phosphatases were characterized by (a) the use of five different 32P-labelled substrate proteins (phosphorylase a, histone H2B, casein, and the alpha and beta subunits of phosphorylase kinase), (b) their behaviour during ion-exchange chromatography, (c) their relative molecular mass distribution during gel filtration, (d) their sensitivity towards inhibition by inhibitor 2, (e) their ability to be stimulated by protamine and (f) by their behaviour during freezing and thawing in the presence of 2-mercaptoethanol. The following results were obtained. 1. The 'cytosol' (100,000 X g supernatant) contains protein phosphatases of the types 1, 2A and 2B. 2. On the basis of inhibition with inhibitor 2 (1.2 micrograms/ml) the 'cytosolic' phosphorylase phosphatase activity consists to about 40% of protein phosphatase 1 and to about 60% of protein phosphatase 2A. 3. In the cytosol about 80-90% of the protein phosphatases 1 and 2A exist in an inactive state. 4. A 5-10-fold activation can be achieved by ethanol precipitation, which results in the generation of a mixture of forms of low apparent molecular mass of about 30 kDa. 5. Microsome-associated phosphorylase phosphatase activities can be extracted in a highly active state by detergent (1% Triton X-100) or by 0.8 M NaCl. 6. Activity measurements in the presence of inhibitor 2 (1.2 micrograms/ml) indicate that the microsomal activities consist to about 75% of protein phosphatase 1 and to about 25% of protein phosphatase 2A. Activities corresponding to protein phosphatases 2B and 2C could not be detected. 7. The 'microsomal' protein phosphatase activities exhibit lower apparent molecular masses (70 kDa and 30 kDa) than the 'cytosolic' protein phosphatases (about 260 kDa). 8. After ethanol treatment of the microsomal protein phosphatases only activities with apparent molecular masses of about 30 kDa can be detected. These share several similarities with the ethanol-treated cytosolic protein phosphatases. 9. Both cytosolic and microsomal protein phosphatases display activity towards histone H2B and casein.
Eur J Biochem 1987 Sep 01
PMID:Protein phosphatases of the guinea-pig parotid gland. 304 Apr 7

A 2.5 kb clone containing the full-length coding sequence of a type-2A protein phosphatase catalytic subunit has been isolated from a rabbit skeletal muscle cDNA library constructed in lambda gt10. The sequence of the protein deduced from the cDNA contains 309 residues (35.58 kDa). A major mRNA species at 2.0 kb and a minor component at 2.8 kb were visualized by Northern blotting in both skeletal muscle and liver. The type-2A enzyme showed weak homology with mammalian alkaline phosphatases between residues 55 and 95. The protein sequence of the type-2A phosphatase from rabbit skeletal muscle differs from that reported for the bovine adrenal enzyme in three regions.
FEBS Lett 1987 Sep 14
PMID:Isolation and sequence analysis of a cDNA clone encoding the entire catalytic subunit of a type-2A protein phosphatase. 304 Apr 74

Highly purified plasma membranes from Y-1 mouse adrenal tumor cells and those from bovine fasciculata cells were shown by [125I]iodocalmodulin overlay to contain five calmodulin-binding proteins of 240,000, 150,000, 66,000, 60,000, and 51,000 mol wt (Mr). Three of these proteins were also detected by affinity chromatography on calmodulin-Sepharose. Calmodulin binding was inhibited by competition with unlabeled calmodulin and by an inhibitor of calmodulin (trifluoperazine). Binding to each of the proteins was Ca2+ dependent. The relative proportion of binding to each of the five proteins was very different for Y-1 and bovine membranes. In Y-1 membranes as much as 50% of total binding was to the 51,000 Mr protein, whereas in bovine membranes more than 50% of binding occurred with the 150,000 Mr protein. Three of the five proteins were tentatively identified as follows: the 240,000 Mr protein is alpha-spectrin, the 60,000 Mr protein is the A subunit of the Ca2+/calmodulin-dependent protein phosphatase called calcineurin and the 51,000 Mr protein is the major subunit of a Ca2+/calmodulin-dependent protein kinase. The kinase was shown to act on specific substrates. It is concluded that calmodulin, by binding to the kinase and phosphatase, is capable of influencing the degree of phosphorylation of specific substrates in the plasma membranes of adrenal cells, and by binding to alpha-spectrin it may influence the cytoskeletons of these cells. These effects of calmodulin are likely to be important in the regulation of steroid synthesis in the adrenal cortex.
Endocrinology 1987 Sep
PMID:Calmodulin-binding proteins in plasma membranes from adrenocortical cells. 362 83

"Heavy" sarcoplasmic reticulum vesicles loaded with 5 mM CaCl2 in the presence of protease inhibitors were phosphorylated by addition of MgATP in the presence or absence of calmodulin. The major site of phosphorylation was a 60-kDa protein. In the absence of added calmodulin, phosphorylation of the 60-kDa protein reached its maximal value (8 pmol of P/mg of membrane protein) at 1 min. In the presence of 1 microM calmodulin, a 2-fold higher level of phosphorylation (16.1 pmol of P/mg of sarcoplasmic reticulum) was reached within a shorter time (10 s). The phosphoprotein was then spontaneously dephosphorylated. The initial rate of Ca2+ release, which was induced by a Ca2+ jump and determined by stopped-flow fluorometry using chlorotetracycline, decreased upon phosphorylation, whereas it was restored upon dephosphorylation. There was good correlation between the amount of P incorporation into the 60-kDa protein and the extent of inhibition of Ca2+ release. In the presence of added calmodulin the protein kinase activity sharply increased in the [Ca2+] range of 0.2-2 microM with a concentration for half-maximal activation at 0.6 microM. On the other hand, the protein phosphatase activity was virtually independent of calmodulin and [Ca2+] in the [Ca2+] range in which protein kinase was activated. The results suggest that the calmodulin-dependent phosphorylation of the 60-kDa protein plays an important role in the regulation of Ca2+ release from sarcoplasmic reticulum.
J Biol Chem 1986 Sep 05
PMID:Involvement of 60-kilodalton phosphoprotein in the regulation of calcium release from skeletal muscle sarcoplasmic reticulum. 374 63

Calcineurin, originally identified as a calmodulin-dependent phosphoprotein phosphatase (Stewart, A.A. et al. (1982) FEBS Lett. 137, 80-84) also uses p-nitrophenyl phosphate and phosphotyrosine as substrates (Pallen, C.J. and Wang, J.H. (1983) J. Biol. Chem. 258, 8550-8553). We have surveyed a wide range of nonprotein phosphocompounds and found that several synthetic aryl phosphocompounds serve as calcineurin substrates. Among more than 20 naturally occurring phosphocompounds tested, only phosphoenol pyruvate possesses significant calcineurin substrate activity. The phosphoenol pyruvate phosphatase activity is dependent on Ni2+ and Mn2+, is stimulated by calmodulin, and is inhibited by a monoclonal antibody to calcineurin, thus indicating that it is an intrinsic property of calcineurin. The results suggest that functional roles of calcineurin may include actions of the enzyme toward nonprotein phosphocompounds.
Biochem Biophys Res Commun 1985 Sep 30
PMID:Survey of calcineurin activity towards nonprotein compounds and identification of phosphoenol pyruvate as a substrate. 405 87

Compared with several other enveloped viruses, purified virions of frog virus 3 contained a relatively high activity of a protein kinase which catalyzed the phosphorylation of endogenous polypeptides or added substrate proteins. Virions also contained a phosphoprotein phosphatase activity which released phosphate covalently linked to proteins. It was possible to select reaction conditions where turnover of protein phosphoesters was minimal, as the phosphatase required Mn(2+) ions for activity whereas the protein kinase was active in the presence of Mg(2+) ions. Electrophoretic studies in polyacrylamide gels containing sodium dodecyl sulfate indicated that at least 10 of the virion polypeptides were phosphorylated in the in vitro protein kinase reaction. Characterization of these phosphoproteins demonstrated that the phosphate was incorporated predominantly in a phosphoester linkage with serine residues. The protein kinase was solubilized by disrupting purified virions with a nonionic detergent in a high-ionic-strength buffer and was separated from many of the virion substrate proteins by zonal centrifugation in glycerol gradients. The partially purified protein kinase would phosphorylate polypeptides of many different animal viruses, and maximal activity was not dependent on added cyclic nucleotides. These properties distinguished the virion protein kinase from a well characterized cyclic AMP-dependent protein kinase which phosphorylated viral proteins only to a small extent.
J Virol 1973 Sep
PMID:Phosphorylation of animal virus proteins by a virion protein kinase. 435 52

Cytosolic protein phosphotyrosine (PPT) phosphatase was measured using a new substrate, Tyr(32P)-labeled bovine serum albumin. Kidney was found as a particularly rich tissue source of PPT-phosphatase activity, containing twice as much as liver and over 10-fold more than brain, heart, lung, or skeletal muscle. An affinity column of Zn2+-iminodiacetate agarose adsorbed up to 60% of the PPT-phosphatase present in kidney extracts. Subsequent chromatography on DEAE-Sepharose separated the phosphatase into two peaks, labeled I and II, that had Mr = 34,000 and 37,000, respectively, upon gel filtration with Sephadex G-75 Superfine. Overall purification of 850- and 1100-fold was achieved with a net 4% yield. Both phosphatases hydrolyzed p-nitrophenylphosphate as well as the protein substrate in the presence of EDTA. Peak I phosphatase activity displayed a neutral pH optimum, had an absolute requirement for sulfhydryl compounds, and was sensitive to trypsin, whereas Peak II activity had an acidic pH optimum and was active without mercaptans. The two proteins also gave different fragmentation patterns by gel electrophoresis after digestion with S. aureus V8 protease. The results show that multiple forms of PPT phosphatase specifically interact with Zn2+ and provide a basis for further structural and functional comparisons among different members of the phosphoprotein phosphatase family.
J Biol Chem 1984 Sep 25
PMID:Cytosolic protein phosphotyrosine phosphatases from rabbit kidney. Purification of two distinct enzymes that bind to Zn2+-iminodiacetate agarose. 608 42


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