| Popis: |
The existence of an Na+, K+ -activated ATPase (Mg2+-dependent, Na+, K+-activated ATP-phosphohydrolase, Ec 3.6.1.3) was discovered by Skou in 1957. Soon afterwards he also found that cardiac glycosides are able to inhibit ATPase activity by binding to the enzyme (Skou, 1960). Extensive work was done by different groups to purify and characterize this enzyme which is specifically associated with active cation transport. Recently the molecular weight of the enzyme, which is composed of two types of polypeptide chain, was found to be 250,000 daltons (Hopkins et al.,1976). The first chain has a molecular weight of 95,000 daltons and contains both an aspartic acid residue that becomes phosphorylated during the transport reaction as well as a binding site for ouabain (Bastide et al., 1973). The second polypeptide has a molecular weight of 50,000 daltons and is characterized as being a glycoprotein (Kyte, 1972). There appear to be one ouabain binding site and either one or two phosphorylation sites per 250,000 daltons molecular weight (Wilson, 1978). |
