Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.3.1 (Mg2+-ATPase)
 1,484 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Reactive disulfide reagents (RDSs) with a biotin moiety have been synthesized and found to cause Ca2+ release from sarcoplasmic reticulum (SR) vesicles. The RDSs oxidize SH sites on SR proteins via a thiol-disulfide exchange, with the formation of mixed disulfide bonds between SR proteins and biotin. Biotinylated RDSs identified a 106-kDa protein which was purified by biotin-avidin chromatography. Disulfide reducing agents, like dithiothreitol, reverse the effect of RDSs and thus promoted active re-uptake of Ca2+ and dissociated biotin from the labeled protein indicating that biotin was covalently linked to the 106-kDa protein via a disulfide bond. Several lines of evidence indicate that this protein is not Ca2+, Mg2+-ATPase and is not a proteolytic fragment or a subunit of the 400-kDa Ca2+-ryanodine receptor complex (RRC). Monoclonal antibodies against the ATPase did not cross-react with the 106-kDa protein, and polyclonal antibodies against the 106-kDa did not cross-react with either the ATPase or the 400-kDa RRC. RDSs did not label the 400-kDa RRC with biotin. Linear sucrose gradients used to purify the RRC show that the 106-kDa protein migrated throughout 5-20% linear sucrose gradients, including the high sucrose density protein fractions containing 400-kDa RRC. Protease inhibitors diisopropylfluorophosphate used to prevent proteolysis of 400-kDa proteins did not alter the migration of 106-kDa in sucrose gradients nor the patterns of biotin labeling of the 106-kDa protein. Incorporation of highly purified 106-kDa protein (free of RRC) in planar bilayers revealed cationic channels with large Na+ (gNa+ = 375 +/- 15 pS) and Ca2+ (gCa2+ = 107.7 +/- 12 pS) conductances which were activated by micromolar [Ca2+]free or millimolar [ATP] and blocked by micromolar ruthenium red or millimolar [Mg2+]. Thus, the SR contains a sulfhydryl-activated 106-kDa Ca2+ channel with apparently similar characteristics to the 400-kDa "feet" proteins.
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PMID:Disulfide linkage of biotin identifies a 106-kDa Ca2+ release channel in sarcoplasmic reticulum. 248 Sep 55

Tryptic modification appears to potentiate activation of the Ca2+ channels of isolated sarcoplasmic reticulum vesicles. In the presence of 1 mM free Mg2+ we observe that: 1) cAMP and doxorubicin activation of passive efflux from tryptically modified vesicles is approximately 20-fold greater than from native SR. 2) Ruthenium red inhibits Ca2+ efflux from modified vesicles. 3) The binding affinities and Hill coefficients of activation of efflux by cAMP and doxorubicin are the same in modified vesicles as in native vesicles. 4) Proteolysis stimulates passive efflux from heavy SR much more than from light SR. 5) Stimulation of cAMP- and doxorubicin-activated Ca2+ release is biphasic, whereas Hg2+-activated Ca2+ efflux is monophasic. 6) In the absence of Mg2+, the Ca2+ dependence of cAMP-activated efflux from tryptically modified vesicles is similar to that of native vesicles, with peak efflux rates occurring between approximately 1 and 10 microM Ca2+. 7) The Mg2+ dependence of efflux from modified vesicles is similar to that of native vesicles. 8) SDS-polyacrylamide gels indicate that the Ca2+, Mg2+-ATPase and the high molecular weight ryanodine receptor are both cleaved faster than the stimulation of efflux.
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PMID:Limited tryptic modification stimulates activation of Ca2+ release from isolated sarcoplasmic reticulum vesicles. 284 65

Elevation of cytosolic calcium levels has been shown to occur via oxidation of critical protein thiols in liver microsomes. Elevated cytosolic Ca2+ may also result from activation of calcium releasing channels. In the presence of NADPH or ascorbic acid, iron ions produced a concentration-dependent release of calcium from liver microsomes. Under anaerobic conditions, the iron-induced release of calcium was inhibited, suggesting that a reaction of oxidation triggers the releasing process. The calcium releasing process at pH 7.0 appears to be highly sensitive to activation by iron ions, as effective concentrations (e.g., 2-5 microM) did not alter the Ca2+, Mg2+-ATPase or the phospholipid component of the microsomal membranes. Iron-induced Ca2+-release could occur under conditions in which there was no iron-induced microsomal lipid peroxidation. Under conditions of intense lipid peroxidation, PBN fully prevented the iron-induced accumulation of thiobarbituric reactive reagents without affecting the release of Ca2+, suggesting that lipid peroxidation is not the mechanism by which iron causes release of calcium. Trolox, GSH and high concentrations of ascorbate, however, strongly inhibited the iron-induced calcium release, most likely due to modulation of the Fe2+/Fe3+ ratio. While the IP3 receptor system is considered to be the main regulator of calcium release, liver also contains a ryanodine-sensitive calcium releasing store. The iron-induced calcium release at pH 7.0 was blocked by ruthenium red, a specific inhibitor of the ryanodine receptor, and Fe2+ (but not Fe3+) decreased the binding of ryanodine, a specific ligand for the ryanodine-sensitive calcium channel. These results suggest that redox-cycling of iron ions results in an activation of a ryanodine-sensitive calcium channel. Activation of calcium releasing channels by iron may play a role in the evolution of various hepatic disorders that are associated with chronic iron overload in humans.
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PMID:Redox-cycling of iron ions triggers calcium release from liver microsomes. 958 5

The immunophilin FKBP12 associates with intracellular Ca2+ channels and this interaction can be disrupted by the immunosuppressant FK506. We have investigated the effect of FK506 on Ca2+ release and Ca2+ uptake in permeabilized cell types. Changes in medium free [Ca2+] were detected by the fluorescent Ca2+ indicator fluo-3 in digitonin-permeabilized SH-SY5Y human neuroblastoma cells, DT40 and R23-11 (i.e. triple inositol 1,4,5-trisphosphate (IP3) receptor knockout cells) chicken B lymphocytes and differentiated and undifferentiated BC3H1 skeletal muscle cells. 45Ca2+ fluxes were studied in saponin-permeabilized A7r5 rat smooth muscle cells. Addition of FK506 to permeabilized SH-SY5Y cells led to a sustained elevation of the medium [Ca2+] corresponding to approximately 30 % of the Ca2+ ionophore A23187-induced [Ca2+] rise. This rise in [Ca2+] was not dependent on mitochondrial activity. This FK506-induced [Ca2+] rise was related to the inhibition of the sarcoplasmic/endoplasmic reticulum Ca2+-Mg2+-ATPase (SERCA) Ca2+ pump. Oxalate-facilitated 45Ca2+ uptake in SH-SY5Y microsomes was inhibited by FK506 with an IC50 of 19 microM. The inhibition of the SERCA Ca2+ pump was not specific since several macrocyclic lactone compounds (ivermectin > FK506, ascomycin and rapamycin) were able to inhibit Ca2+ uptake activity. FK506 (10 microM) did not affect IP3-induced Ca2+ release in permeabilized SH-SY5Y and A7r5 cells, but enhanced caffeine-induced Ca2+ release via the ryanodine receptor (RyR) in differentiated BC3H1 cells. In conclusion, FK506 inhibited active Ca2+ uptake by the SERCA Ca2+ pump; in addition, FK506 enhanced intracellular Ca2+ release through the RyR, but it had no direct effect on IP3-induced Ca2+ release.
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PMID:Effects of the immunosuppressant FK506 on intracellular Ca2+ release and Ca2+ accumulation mechanisms. 1085 21