Isolation and structural properties of membrane-bound Na+,K+- adenosine triphosphatase from pig kidney]

A technique for isolation of large amounts of homogeneous Na+, K+-ATPase lipid-protein complex from pig kindney has been developed. The purity of the preparation as determined by the protein component is 96-98%, the large to small subparticle ratio being 4 : 1. The protein and lipid parts of the preparation have approximately the same mass. The enzyme activity is 1600-1900 mcmoles of inorganic phosphate released per mg of protein per hour. The protein secondary structure in a heavy water solution has been studied by infrared spectroscopy in the region of the main amide bands. It has been shown that about 20% of the peptide groups form highly ordered alpha-helical regions and about 25% are found in the pleated sheet structure with an antiparallel packing of the chains. The regions with a regular structure are mainly located in the protein component regions, inaccessible for water and are presumably involved in the formation of the hydrophobic core of the molecule. The major part of the protein structure (approximately 55%) is non-ordered and is easily accessible for water molecules.