title: Effects of ATP and magnesium ions on the fluorescence of harmala alkaloids. Restrictions for the use of harmala alkaloids as fluorescent probes for (Na+ + K+)-ATPase.
abstract: 1. Harmine and harmaline were investigated as potentially useful fluorescent inhibitors of (Na+ + K+) activated ATPase. 29 From spectroscopic measurements both compounds were shown to form 1 : 1 complexes with ATP, the dissociation constants being 0.65 mM and 1.83 mM for harmine and harmaline respectively. Addition of Mg2+ and enzyme further affected these equilibria. 3. Although it was possible to demonstrate a competitive effect of harmine at the sodium-loading site of the enzyme, other inhibitory effects, including inhibitions of ouabain binding and the ouabain-insensitive ATPase were found. 4. It was concluded that the harmala alkaloids can inhibit (Na+ + K+)-activated ATPase in a complex way involving both Na- and ATP-binding sites. This severely limits their usefulness as spectroscopic probes.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology*; D004789:Enzyme Activation / Q000187:drug effects; D006246:Harmaline / Q000494:pharmacology; D006247:Harmine / Q000494:pharmacology; D007672:Kidney Cortex / Q000201:enzymology; D007679:Kidney Medulla / Q000201:enzymology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008433:Mathematics; D010042:Ouabain / Q000494:pharmacology; D011485:Protein Binding; D013050:Spectrometry, Fluorescence; D013552:Swine
chemical_list: D000470:Alkaloids; D006247:Harmine; D010042:Ouabain; D000255:Adenosine Triphosphate; D006246:Harmaline; D000251:Adenosine Triphosphatases; D008274:Magnesium