[Molecular organization of Mg2+, Ca2+-ATPase of sarcoplasmic reticulum].

The article deals with the results of studies on the structure and properties of discrete sites in a molecule of sarcoplasmic reticulum Mg2+, Ca2+-ATPase obtained during its fragmentation in the process of its limited hydrolysis by trypsin. It is established to contain three fragments with the molecular mass of 45 000, 30 000 and 20 000 Daltons. Some properties of these fragments are determined by the amino acid analysis, inhibitory analysis with application of radiactive labels and also of immunochemical analysis. The properties show that the first fragment is hydrophobic and the others are hydrophilic; these properties show that the first fragment is hydrophobic and the others are hydrophilic; these properties determine the location of the fragments in the sarcoplasmic reticulum membrane. The fragment with the molecular mass of 45 000 Daltons forms in it a nonspecific channel as if "sewing" it, two other fragments of the Mg2+, Ca2+-ATPase are located at the outer side of the membrane, the fragment with the molecular weight of 20 000 occupying a middle position between the fragments with molecular weight of 45 000 and 30 000, thus creating a selective respect to calcium "valve" to the nonspecific channel. This discrete part of Mg2+, Ca2+-ATPase possesses the ionophoric activity. The fragment with molecular weight of 30 000 is the energy converter. The site hydrolyzing AMP is located in it. The models (hypothetic) are presented for the Ca2+ active transpprt through biological membranes with Mg2+, Ca2+-ATPase participation.