Properties of the Two Polypeptides of Sodium- and Potassium-dependent Adenosine Triphosphatase

Abstract

Abstract The (Na+ + K+)-dependent adenosine triphosphatase from canine renal medulla is composed of lipids and of two polypeptide chains. The larger one has a molecular weight of 135,000, NH2-terminal glycine, and has a high content of non-polar amino acids. The smaller polypeptide chain has NH2-terminal alanine and it is a sialoglycoprotein. The two polypeptides are present in a mass ratio of 1.7:1 for the ratio of large to small chain. This mass ratio probably corresponds to a molar ratio of one large chain to two small chains. The two chains are close to one another in the purified enzyme because they can be covalently crosslinked by dimethyl suberimidate. Finally, the large polypeptide chain, which has all of the properties of a membrane-bound enzyme, is soluble in simple aqueous solvents in the absence of detergents and lipids, although it no longer has enzymatic activity.