Inhibition of the intracellular Ca^sup 2+^ transporter SERCA (Sarco-Endoplasmic Reticulum Ca^sup 2+^-ATPase) by the natural polyphenol epigallocatechin-3-gallate

• Published in: Journal of bioenergetics and biomembranes 2012-10, Vol.44 (5), p.597
• Main Authors: Soler, Fernando, Asensio, M Carmen, Fernández-belda, Francisco
• Format: Article
• Language: English
• Subjects: Adenosine triphosphatase; ATP; Binding sites; Enzymes; Musculoskeletal system; Phosphorylation; Transport processes
• ISSN: 0145-479X; 1573-6881
• DOI: 10.1007/s10863-012-9462-z

The use of a microsomal preparation from skeletal muscle revealed that both Ca^sup 2+^ transport and Ca^sup 2+^-dependent ATP hydrolysis linked to Sarco-Endoplasmic Reticulum Ca^sup 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^sup 2+^-ATPase activity decreased when the Ca^sup 2+^ concentration was raised but not when the ATP concentration was elevated. Data on the catalytic cycle indicated inhibition of maximal Ca^sup 2+^ binding and a decrease in Ca^sup 2+^ binding affinity when measured in the absence of ATP. Moreover, the addition of ATP to samples in the presence of EGCG and Ca^sup 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^sup 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^sup 2+^-free state, thus impeding Ca^sup 2+^ binding and therefore the subsequent steps when ATP is added to trigger the Ca^sup 2+^ transport process. Furthermore, phosphorylation by inorganic phosphate in the absence of Ca^sup 2+^ was partially inhibited by EGCG, suggesting alteration of the native Ca^sup 2+^-free conformation at the catalytic site.[PUBLICATION ABSTRACT]