Many membrane proteins become labile when they are solubilized by detergent. Here we show that the presence of high concentrations of glycyl betaine stabilizes one of these proteins, the sarcoplasmic reticulum Ca2+-ATPase (SERCA1a), solubilized with nonionic detergents like n-dodecyl beta-D-Maltopyranoside (DDM) or octaethylene glycol monododecyl ether (C12E8) which are commonly used for its purification or crystallization. Betaine at high concentrations might become useful as a stabilizing agent for detergent-solubilized membrane proteins, for instance during purification procedures or during the long periods of time required for crystallogenesis. (C) 2009 Elsevier Inc. All rights reserved.