title: Turnover and regulation of Na-K-ATPase in HeLa cells.
abstract: HeLa cells in log growth have 10(6) surface Na-K-ATPase molecules as estimated by the specific binding of [3H]-ouabain. Studies utilizing ouabain as a label show that the ligand is internalized at a rate corresponding to the turnover of three sets of Na-K-ATPase enzymes per generation. The label is taken up exclusively into a particulate cell compartment where it is codistributed with beta-hexosaminidase, identifying the internal compartment as lysosomal. Turnover is an important parameter in the recovery of the cells from glycoside intoxication. The unmetabolized glycoside is subsequently released by exocytosis. 13C-density-labeled Na-K-ATPase has been identified by specific phosphorylation of its catalytic subunit with [32P]ATP or [33P]ATP, and the rate of turnover of the density label is shown to be the same as the internalization of the ouabain-labeled site. There is a transit time of about 4 h from the onset of synthesis of the catalytic subunit to its insertion in the surface membrane; 2,800 catalytic subunits are synthesized per minute per cell, and 2,100 are turned over K+-starved cells respond to the stress in 24-30 h with modulation of the surface density of Na-K-ATPase the synthetic rate remains constant; the number of functional enzymes per cell is controlled by change in the rate constant for turnover.
mesh_terms: D002455:Cell Division; D002462:Cell Membrane / Q000201:enzymology; D005089:Exocytosis; D006367:HeLa Cells / Q000201:enzymology* / Q000502:physiology; D006801:Humans; D007700:Kinetics; D010042:Ouabain / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D011485:Protein Binding; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium