Brominated Lipids and Detergents Effects on SERCA1a

Brominated phosphatidylcholine (BrPC, 1,2-di-(9,10-dibromo)stearoyl-sn-glycero-3-phosphocholine, #850366) and egg phosphatidylcholine (#840051) were from Avanti Polar Lipids, DDM (n-dodecyl-β-D-maltoside) and C₁₂E₈ (octaethylene glycol monododecyl ether) were from Anatrace, and other chemicals were of standard grade. SERCA1a-containing sarcoplasmic reticulum (SR) membranes (with lipid and protein contents of about 0.5 g lipid per g protein [15 (link)]) were prepared from rabbit skeletal muscle as described [16 (link)]. Streptavidin-purified yeast Drs2p/Cdc50p complex was also prepared as described [17 (link)]. Brominated DDM (BrDDM, 5,6-dibromo-dodecyl-β-D-maltoside) was synthesized as described [18 ]; its critical micelle concentration (cmc), measured according to the methyl orange method [19 (link)], was found only 20% higher than that for DDM (see similar result with 7–8 BrDDM in [14 ]), and BrDDM affected SERCA1a ATPase activity in a manner very similar to DDM (S1 Fig). Two different buffers were used, either buffer A (100 mM KCl, 1 mM MgCl₂, 50 mM Tes-Tris at pH 7.5 and 0.1 mM CaCl₂), or buffer B (100 mM KCl, 5 mM MgCl₂, 50 mM Mops-Tris at pH 7 and contaminating Ca²⁺ from demineralized water, a few micromolar).