Separation of membranes from acid-solubilized fish muscle proteins with the aid of calcium ions and organic acids.

Calcium chloride, and to a lesser extent MgCl 2 , aided in the separation of membranes by centrifugation from cod (Gadus morhua) muscle homogenates solubilized at pH 3 in the presence of citric acid or malic acid but not lactic acid. Adding citric acid and Ca 2 + before solubilizing the cod muscle homogenates was needed for the effect. At 1 mM citric acid, 70-80% of the phospholipid and 25-30% of the protein were removed at 10 mM Ca 2 + . At 8 mM Ca 2 + , citric acid showed an optimal effect on phospholipid removal at 5 mM with 90% of the phospholipid and 35% of the protein removed. The treatment with citric acid and Ca 2 + was also effective in separating the membrane from solubilized herring (Clupea harengus) muscle homogenate. Ca 2 + and citric acid might exert their influence by disconnecting linkages between membranes and cytoskeletal proteins.