title: Inhibition of the intracellular Ca(2+) transporter SERCA (Sarco-Endoplasmic Reticulum Ca(2+)-ATPase) by the natural polyphenol epigallocatechin-3-gallate.
abstract: The use of a microsomal preparation from skeletal muscle revealed that both Ca(2+) transport and Ca(2+)-dependent ATP hydrolysis linked to Sarco-Endoplasmic Reticulum Ca(2+)-ATPase are inhibited by epigallocatechin-3-gallate (EGCG). A half-maximal effect was achieved at approx. 12 μM. The presence of the galloyl group was essential for the inhibitory effect of the catechin. The relative inhibition of the Ca(2+)-ATPase activity decreased when the Ca(2+) concentration was raised but not when the ATP concentration was elevated. Data on the catalytic cycle indicated inhibition of maximal Ca(2+) binding and a decrease in Ca(2+) binding affinity when measured in the absence of ATP. Moreover, the addition of ATP to samples in the presence of EGCG and Ca(2+) led to an early increase in phosphoenzyme followed by a time-dependent decay that was faster when the drug concentration was raised. However, phosphorylation following the addition of ATP plus Ca(2+) led to a slow rate of phosphoenzyme accumulation that was also dependent on EGCG concentration. The results are consistent with retention of the transporter conformation in the Ca(2+)-free state, thus impeding Ca(2+) binding and therefore the subsequent steps when ATP is added to trigger the Ca(2+) transport process. Furthermore, phosphorylation by inorganic phosphate in the absence of Ca(2+) was partially inhibited by EGCG, suggesting alteration of the native Ca(2+)-free conformation at the catalytic site.
authors.affiliation: Departamento de Bioquímica y Biología Molecular A, Universidad de Murcia, Campus de Espinardo, Murcia, Spain.
authors.forename: Fernando
authors.initials: F
authors.lastname: Soler
authors.forename: M Carmen
authors.initials: MC
authors.lastname: Asensio
authors.forename: Francisco
authors.initials: F
authors.lastname: Fernández-Belda
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002392:Catechin / Q000031:analogs & derivatives* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D008861:Microsomes / Q000201:enzymology*; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000201:enzymology*; D010710:Phosphates / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011817:Rabbits; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D000975:Antioxidants; D009124:Muscle Proteins; D010710:Phosphates; D000255:Adenosine Triphosphate; D002392:Catechin; C045651:epigallocatechin gallate; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002118:Calcium