Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.13 (protein kinase C)
 49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The intracellular events and specifically the role of protein kinase C-mediated protein phosphorylation, after alpha-adrenergic receptor stimulation of the heart, are not well understood. We examined the phosphorylation of sarcolemmal, sarcoplasmic reticular, myofibrillar, and cytosolic proteins in perfused beating rabbit hearts on activation of protein kinase C by phenylephrine. Perfusion of rabbit hearts with phenylephrine was associated with a positive inotropic response, which was dose and time dependent. Maximal stimulation (1.54-fold increase in +dP/dt) was obtained with 10 microM phenylephrine at 4 minutes. Examination of the activity levels of protein kinase C in these hearts revealed a redistribution of this activity from the cytosolic to the membranous fraction, suggesting the activation of this enzyme in vivo. Prazosin, an alpha 1-adrenergic antagonist, prevented the increase in the inotropy and the redistribution of protein kinase C activity mediated by phenylephrine. Examination of the degree of phosphorylation of membranous, myofibrillar, and cytosolic proteins revealed that activation of protein kinase C in vivo was associated with increased phosphorylation of a 15-kd sarcolemmal protein and a 28-kd cytosolic protein. There were no increases in the degree of phosphorylation of phospholamban in the sarcoplasmic reticulum and of troponin I, troponin T, and C protein in the myofibrils, although these proteins were found to be substrates for protein kinase C in vitro. These findings provide evidence that protein kinase C is activated in response to alpha-adrenergic stimulation and that activation is associated with increased phosphorylation of a 15-kd sarcolemmal protein and a 28-kd cytosolic protein in the myocardium.
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PMID:Effect of alpha-adrenergic stimulation on activation of protein kinase C and phosphorylation of proteins in intact rabbit hearts. 131 11

Many neurohormones alter the force of cardiac contraction by variations in the intracellular Ca2+ concentration. alpha 1-Adrenergic and muscarinic stimulations, rather, modify the sensitivity of contractile proteins to Ca(2+)-calmodulin-myosin light-chain kinase (MLCK) complex induces a large increase in Ca2+ sensitivity (0.14 pCa unit) of these easily accessible myofilaments. This increase is further enhanced by up to 0.19 pCa unit when protein kinase C (PKC) is added together with MLCK. Similarly, the Ca2+ ATPase activity of skinned cells in suspension is increased in the presence of MLCK and further in the presence of both kinases. 32P-labelling and SDS/PAGE show that these changes are associated with light-chain 2 (LC2) phosphorylation together with phosphorylation of troponin I and troponin T when PKC is added. Although to a smaller extent than in smooth muscle, phosphorylation of cardiac myosin LC2 may be involved in the modulation of heart contractility.
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PMID:Protein kinase C enhances myosin light-chain kinase effects on force development and ATPase activity in rat single skinned cardiac cells. 138 18

Effects of phosphorylation of bovine cardiac troponin T (TnT) by protein kinase C on the Ca(2+)-stimulated MgATPase activity of reconstituted actomyosin complex and the binding of TnT to tropomyosin(Tm)-F-actin were investigated. The Ca(2+)-stimulated MgATPase of actomyosin containing phosphorylated TnT (1.8 mol of P/mol), compared with that containing unphosphorylated TnT, was decreased by up to 48%. Phosphorylation of TnT also decreased (up to 48%) its maximum binding to Tm-F-actin, which was accompanied by a decrease (up to 3.5-fold) in its apparent binding affinity. The findings indicate that the effects of phosphorylated TnT in decreasing actomyosin MgATPase might be secondary to its decreased interactions with the other components of the thin filament, representing a new mechanism underlying the negative inotropic responses of various cardiac preparations to protein kinase C-activating phorbol esters.
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PMID:Protein kinase C phosphorylation of cardiac troponin T decreases Ca(2+)-dependent actomyosin MgATPase activity and troponin T binding to tropomyosin-F-actin complex. 144 57

Effects of troponin phosphorylation on Ca2(+)-stimulated MgATPase activity of bovine cardiac actomyosin were examined. Phosphorylation by protein kinase C of troponin I and troponin T subunits in troponin or troponin-tropomyosin complex resulted in a decreased Ca2(+)-stimulated MgATPase activity in reconstituted actomyosin, and this effect was reversed by subsequent dephosphorylation by protein phosphatase 1. It was further observed that protein kinase C phosphorylation of either troponin I or troponin T subunits led to a similar inhibition of Ca2(+)-stimulated actomyosin MgATPase activity. In all cases, EC50 values (concentrations causing 50% stimulation) for Ca2+ were not appreciably affected by troponin phosphorylation by protein kinase C. Data from phosphorylation site analysis suggests that phosphorylation of threonine 144 in troponin I and possibly threonine 280 or threonine 199 in troponin T might be important for the observed decrease of Ca2(+)-stimulated actomyosin MgATPase. It is suggested that inhibition of actomyosin MgATPase caused by protein kinase C phosphorylation of troponin I and/or troponin T represents a new mechanism that can account for in part the reported negative inotropic effect of phorbol esters on various cardiac preparations.
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PMID:Protein kinase C phosphorylation of cardiac troponin I or troponin T inhibits Ca2(+)-stimulated actomyosin MgATPase activity. 182 28

As an extension of our previous reports that cardiac and skeletal muscle troponin I (Tn-I) and troponin T (Tn-T) are excellent substrates for protein kinase C (PKC) (Katoh, N., Wise, B. C., and Kuo, J. F. (1983) Biochem. J. 209, 189-195; Mazzei, G. J., and Kuo, J. F. (1984) Biochem. J. 218, 361-369), we have now determined that PKC phosphorylated serine 43 (and/or serine 45), serine 78, and threonine 144 in the free Tn-I subunit and threonine 190, threonine 199, and threonine 280 in the free Tn-T subunit of bovine cardiac troponin. PKC appeared to phosphorylate the same sites of the subunits present in the form of the troponin complex, as indicated by the similarity in the two-dimensional phosphopeptide maps. Although some of the phosphorylation sites were shared by other classes of protein kinases, PKC exhibited a distinct substrate specificity. It was also noted that phosphorylated serine and threonine residues in Tn-I and Tn-T had neighboring basic amino acid residues separated by 1 or 2 other residues both at the amino and carboxyl termini, in agreement with the conclusion of House et al. (House, C., Wettenhall, R. E. H., and Kemp, B. E. (1987) J. Biol. Chem. 262, 772-777) based upon their studies on other substrate proteins. Several peptides having sequences around the phosphorylating sites have been synthesized. The phosphorylation experiments indicated that these peptides were substrates for PKC, and their relative substrate activity (determined by the ratios of Vmax/Km) compared with other proteins, in descending order, was Tn-I = Tn-I(134-154) greater than Tn-T much greater than histone H1 greater than Tn-I(33-35) approximately Tn-T(268-284) greater than Tn-T(179-198) approximately Tn-T(191-209). It is suggested that PKC phosphorylation of Tn-I and Tn-T could be biologically significant in terms of possible modifications in interactions among the individual contractile protein components as well as the Ca2+ sensitivity and activity of actomyosin ATPase.
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PMID:Identification of sites phosphorylated in bovine cardiac troponin I and troponin T by protein kinase C and comparative substrate activity of synthetic peptides containing the phosphorylation sites. 258 39

The phosphorylation of the whole troponin complex and of the cardiac and skeletal troponin components by Ca2+-phospholipid-dependent protein kinase was studied. The activity of enzyme isolated from rat brain by ion-exchange chromatography on DEAE-Sephadex and by affinity chromatography on phosphatidylserine immobilized on polyacrylamide gel was shown to be completely dependent on Ca2+ and phospholipids and was equal to 0.4-0.6 mumol of phosphate/min.mg protein with histone H1 as substrate. The resulting preparation of Ca2+-phospholipid-dependent protein kinase was able to phosphorylate the isolated troponin I; the amount of phosphate transferred per mol of cardiac and skeletal troponin I was equal to 1.1 and 0.4, respectively. The maximal degree of phosphorylation of isolated troponin T by Ca2+-phospholipid-dependent protein kinase was 0.6 mol of phosphate per mol of troponin T both for skeletal and cardiac proteins. The rate and degree of phosphorylation were independent of the initial level of troponin T phosphorylation. Ca2+-phospholipid-dependent protein kinase did not phosphorylate the first serine residue of troponin T, i.e., the site which was phosphorylated in the highest degree after isolation of troponin T from skeletal muscles. The data obtained and the fact that the rate and degree of phosphorylation of troponins I and T within the whole troponin complex are 10-20 times less than those for isolated components provide little evidence for the participation of protein kinase C in troponin phosphorylation in vivo.
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PMID:[Phosphorylation of troponin in the heart and skeletal muscle by Ca2+-phospholipid-dependent protein kinase]. 335 65

Phosphorylation of skeletal and cardiac troponin T by Ca-phospholipid-dependent protein kinase/protein kinase C/was investigated. Under conditions used, the rate of troponin T phosphorylation was only 3-4 times lower than that of histone H-1, and after long term incubation the enzyme incorporated about 1 mol of phosphate per mol of skeletal and cardiac troponin T. The sites phosphorylated by protein kinase C are mainly located in the C-terminal part/residues 159-259/of skeletal troponin T. The less effectively phosphorylated sites are located in between residues 42-158 of troponin T. Reverse phase HPLC revealed four groups of tryptic phosphopeptides of troponin T. The phosphopeptides weakly adsorbed on a RP-18 column were identified as a mixture of two peptides/GKKQTAR and QTAR/both containing Thr-171 of troponin T phosphorylated by protein kinase C.
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PMID:Phosphorylation of troponin T by Ca-phospholipid-dependent protein kinase. 343 4

The inhibitory effects of the phosphorylation of bovine cardiac troponin I (TnI) and troponin T (TnT) by protein kinase C (PKC) on the activity of Ca(2+)-stimulated MgATPase of reconstituted actomyosin complex, as a function of the concentration of myosin or myosin subfragment 1 (S-1), were investigated. Phosphorylation of TnI and/or TnT invariably decreased the Ca(2+)-stimulated enzyme activity of reconstituted actomyosin or actomyosin S-1, regardless of the concentration of whole myosin or S-1. The inhibition due to phosphorylated TnI was partially overcome as the concentration of myosin or S-1 increased, suggesting simple competition of phosphorylated TnI with myosin or S-1 for actin binding sites. Inhibition due to phosphorylated TnT, however, remained constant at all concentrations of myosin or S-1, suggesting that phosphorylated TnT may inhibit full Ca(2+)-activation of the thin filament. Both phosphorylated TnI and TnT inhibited the Ca(2+)-stimulated binding of S-1.ADP to regulated actin, consistent with the notion that the effects of phosphorylation of TnI and TnT affected interactions of the thin filament with the thick filament. Effects of PKC phosphorylation of the contractile components in adult rat cardiac myofibrils were also investigated. PKC phosphorylation of TnI and TnT, as well as other proteins in the contractile complex, resulted in the inhibition of Ca(2+)-stimulated MgATPase activity with little change in the Ca(2+)-sensitivity. Thus, the negative inotropic effects attributable to activation of PKC by phorbol esters, as reported by others, could be explained in part through PKC mediated phosphorylation of components of the contractile apparatus.
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PMID:Protein kinase C phosphorylation of cardiac troponin I and troponin T inhibits Ca(2+)-stimulated MgATPase activity in reconstituted actomyosin and isolated myofibrils, and decreases actin-myosin interactions. 844 Nov 81

Myosin light chain 2 (MLC2) phosphorylation in rat cardiac whole myosin by cardiac myosin light chain kinase (MLCK) or by protein kinase C (PKC) resulted in increased actin-stimulated myosin MgATPase activity. The phosphorylation also increased Ca(2+)-stimulated myofibrillar MgATPase activity upon substitution of the phosphorylated myosin into myofibrils. In addition, phosphorylation of MLC2 in myofibrils by MLCK increased both the Ca(2+)-sensitivity and maximum activity of the myofibrillar Ca(2+)-stimulated MgATPase activity. The latter effect was inhibited by PKC-phosphorylation of troponin I, troponin T and C-protein. A role for both PKC and MLCK in regulating cardiac myofibrillar activity, via phosphorylation of various contractile proteins, is indicated.
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PMID:Phosphorylation of cardiac myosin light chain 2 by protein kinase C and myosin light chain kinase increases Ca(2+)-stimulated actomyosin MgATPase activity. 850 15

We tested the hypothesis that altered phosphorylation of myofibrillar proteins is involved in post-ischemic myocardial stunning. Myofibrillar proteins were isolated from Langendorff perfused control rabbit hearts, hearts submitted to 15 min normothermic ischemia and hearts submitted to 15 min ischemia followed by 10 min of reperfusion (stunned hearts). The in vivo level of phosphorylation of specific contractile proteins by protein kinases A and C was indirectly detected by the amount of 32P incorporated in vitro in the presence of these protein kinases and saturating concentration of [gamma-32P]-ATP (back-phosphorylation method). In control experiments the back-phosphorylation technique was able to detect PKA- or PKC-induced protein phosphorylation in hearts treated with isoproterenol and phorbol ester, respectively. In stunned hearts, contractile function was significantly suppressed compared to the period before ischemia. We found no difference in myofibrillar protein profile (on densitometry of the Coomassie-stained gels after SDS-PAGE) and in PKA mediated 32P incorporation when comparing control, ischemic and stunned myocardium. Three different PKCs were used for phosphorylation: commercial purified rat brain PKC, partially purified rat brain PKC or rabbit partially purified cardiac PKC. Cardiac PKC mainly phosphorylated troponin I, whereas brain PKC phosphorylated both troponin T and troponin I. No significant difference in 32P incorporation mediated by either brain or cardiac PKC was found between control, ischemic and ischemic/reperfused myofibrils. These data indicate that myocardial stunning does not cause changes in PKC- or PKA-mediated Pi incorporation into myofibrillar proteins detectable by the back-phosphorylation method.
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PMID:Phosphorylation by protein kinases A and C of myofibrillar proteins in rabbit stunned and non-stunned myocardium. 944 26


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