Cell surface NADH oxidase activity of brine shrimp oscillates with a period of 25 min and is entrained by light

Surface NADH oxidase of HeLa cells lacks intrinsic membrane binding motifs

Disulfide-thiol interchange proteins with hydroquinone (NADH) oxidase activities (designated NOX for plasma membrane-associated NADH oxidases) occur as extrinsic membrane proteins associated with the plasma membrane at the outer cell surface. The cancer-associated NOX protein, designated tNOX, has been cloned. The 34-kDa plasma membrane-associated form of the protein contains no strongly hydrophobic regions and is not transmembrane. No myristoylation or phosphatidylinositol anchor motifs were discovered. Evidence for lack of involvement of a glycosylphosphatidylinositol-linkage was derived from the inability of treatment with a phosphatidylinositol-specific phospholipase C or with nitrous acid at low pH to release the NOX protein from the surface of HeLa cells or from plasma membranes isolated from HeLa cells. Binding of NOX protein to the plasma membrane via amino acid side chain modification or by attachment of fatty acids also is unlikely based on use of specific fatty acid antisera to protein bound fatty acids and as a result of binding to the cancer cell surface of a truncated form of recombinant tNOX. Incubation of cells or plasma membranes with 0.1 M sodium acetate, pH 5, at 37 degrees C for 1 h, was sufficient to release tNOX from the HeLa cell surface. Release was unaffected by protease inhibitors or divalent ions and was not accelerated by addition of cathepsin D. The findings suggest dissociable receptor binding as a possible basis for their plasma membrane association.

A light-responsive and periodic NADH oxidase activity of the cell surface of Tetrahymena and of human buffy coat cells

Oxidation of external NADH (NADH is an impermeant substrate) by cells of Tetrahymena pyriformis oscillated with a period of 24-26 min. The period length in darkness (25.6 min) appeared to be slightly longer than the period in light (approximately 24 min). When Tetrahymena were placed in darkness for 30-50 min and then returned to light, a new maximum in the rate of NADH oxidation was observed 36-38 min (13 + 24) min after the beginning of the light treatment. The cell-surface NADH oxidase of human buffy coats (a mixture of white cells and platelets) also was periodic and light responsive.