An active preparations of Na+, K+-ATPase containing three types of catalytic isoforms were isolated from the bovine brain to study the structure and function of the sodium pump. It was found, that Na+, K+-ATPase from the brain grey matter was characterized by the biphasic kinetics with respect to ouabain inhibition and consisted of a set of isozymes with subunit composition of α1β1, α2βm and α3βm (where m = 1 and/or 2); moreover, the α1β1 form dominated clearly. For the first time, different glycosylation of the β1-subunit of the α1β1-type isozymes from the kidney and brain was shown. Na+, K+-ATPaSe from the brain stem and axolemma consisted mainly of a mixture of α2β1 and α3β1 isozymes having identical ouabain inhibition constants. In epithelial and arterial smooth muscle cells, in which the plasma membrane is divided into functionally and biochemically distinct domains, the polarized distribution of Na+, K+-ATPase is maintained through interactions with the membrane cytoskeleton proteins ankyrin and spectrin (Nelson & Hammerton, 1989; Lee et al., 1996). We were the first to show the presence of the cytoskeleton protein tubulin (β5-isoform) and glyceraldehyde-3-phosphate dehydrogenase in a high-molecular-weight complex with Na+, K+-ATPase in brain stem neuron cells containing α2β1 and α3β1 isozymes. Consequently the influence of not only subunit composition, but also of glycan and cytoskeleton structures and other plasma membrane-associated proteins on the functional properties of Na+, K+-ATPase isozymes is evident.