Assay of Na,K-ATPase in plasma membrane preparations: increasing the permeability of membrane vesicles using sodium dodecyl sulfate buffered with bovine serum albumin.

Determination of maximal Na,K-ATPase activity in isolated plasma membranes is generally hampered by the vesicular nature of the preparation, limiting access of ATP and ions to one face or the other of the transmembrane protein. Detergents are often used to make the vesicles permeable to the substrates; however, the detergent/protein ratio is extremely critical for optimal activation. The use of bovine serum albumin as a detergent buffer is described. With this method the amount of membrane protein in the assay can be varied over a wide range, with full detergent activation. The method has been used for assay of Na,K-ATPase activity of membranes from dog kidney, rabbit brain, and electric organ of eel.