title: The effect of bilayer thickness on the activity of (Na+ + K+)-ATPase.
abstract: The activities of purified (Na+ + K+)-ATPase supported by a series of phosphatidylcholines with monounsaturated (cis-9) fatty acyl chains (di(n : 1) phosphatidylcholine) varying in length from n = 12 to n = 23 were determined by the lipid titration technique. The ATPase activity at 20 degrees C decreased from 2.9 to 0.1 mumol/min per mg protein as n was decreased from 16 to 12 and decreased from 2.9 to 1.0 mumol/min per mg protein as n was increased from 20 to 23. In further experiments, the di(n : 1) phosphatidylcholine-ATPase complexes were treated with increasing proportions of n-decane, which has been shown previously to increase the thickness of black lipid membranes. n-Decane caused a large increase (greater than 20-fold) in activity of the short-chain complexes (n = 12,13); for n = 14--18, the ATPase activity first increased and subsequently decreased as the proportion of decane was increased, and for n = 20 or 23 decane caused a progressive decrease in activity with increasing concentration. These effects confirm qualitatively that a major factor determining the activity in each bilayer is its thickness. This behaviour closely parallels that of the (Ca2+ + Mg2+)-ATPase of sarcoplasmic reticulum [1] and suggests that a major class of trans-membrane transport proteins may have a similar dependence on bilayer thickness.
mesh_terms: D000473:Alkanes / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D007668:Kidney / Q000201:enzymology*; D008051:Lipid Bilayers / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013552:Swine
chemical_list: D000473:Alkanes; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase; C012867:decane