Two isoenzymes of Na+,K+-ATPase have different kinetics of K+ dephosphorylation in normal cat and human brain cortex.
Analysis of purified Na+,K+-ATPase from cat and human cortex by sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveals two large catalytic subunits called alpha (-) (lower molecular weight) and alpha (+) (higher molecular weight). Differences in K+ dephosphorylation of these two molecular forms have been investigated by measuring the phosphorylation level of each protein after their separation on sodium dodecyl sulfate gels. In the presence of Na+, Mg2+, and ATP, both subunits are phosphorylated. Increasing concentrations (from 0 to 3 mM) of K+ induce progressive dephosphorylation of both alpha-subunits, although the phosphoprotein content of alpha (-) is decreased significantly less than that of alpha (+). Ka values of alpha (-) for K+ are 40% and 50% greater in cat and human cortex, respectively, than values of alpha (+). alpha (-) and alpha (+) are thought to be localized in specific cell types of the brain: alpha (-) is the exclusive form of nonneuronal cells (astrocytes), whereas alpha (+) is the only form of axolemma. Our results support the hypothesis that glial and neuronal Na+,K+-ATPases are different molecular entities differing at least by their K+ sensitivity. Results are discussed in relation to the role of glial cells in the regulation of extracellular K+ in brain.
Guillaume
D
D
Laboratory of Biochemistry, University of Liège, Belgium.
Grisar
T
T
Delgado-Escueta
A V
AV
Laschet
J
J
Bureau-Heeren
M
M
D000818:Animals; D002415:Cats; D002540:Cerebral Cortex / Q000201:enzymology*; D004589:Electrophoresis, Disc; D006801:Humans; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008970:Molecular Weight; D010766:Phosphorylation; D011188:Potassium / Q000494:pharmacology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000302:isolation & purification / Q000378:metabolism*; D013045:Species Specificity
D007527:Isoenzymes; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium