Firefly luciferase can use L-luciferin to produce light.
L-Luciferin is a competitive inhibitor of firefly luciferase with a K1 between 3 and 4 microM. Furthermore L-luciferin can serve as an alternative substrate for light production. Catalysis of L-luciferin can be observed in the absence of, or at low concentrations of, D-luciferin. The light production from L-luciferin increases slowly (maximal half-time 8 min) to a stable plateau. At low concentrations of enzyme and L-luciferin, maximal light production is about half of that observed at corresponding D-luciferin concentrations. Increasing the concentration of enzyme or L-luciferin reduces the light production relative to that obtained by D-luciferin catalysis. In contrast to the catalysis of D-luciferin the light production from L-luciferin can be effectively stimulated by the addition of PP1 provided that luciferase is premixed with inorganic pyrophosphatase (PP1-ase). A flash is emitted if PP1 is injected into a mixture of luciferase, L-luciferin, ATP and PP1-ase. The system maintains its responsiveness and emits further flashes of about equal duration and intensity upon repeated additions of PP1. It is proposed that PP1 induces a racemization of enzyme-bound L-luciferyl adenylate. The potential usefulness of PP1-dependent intracellular ATP monitoring is discussed. The proposed activation of firefly luciferase by PP1 may be part of the regulation of in vivo flashing.
Lembert
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Department of Histology and Cell Biology, Umeå University, Sweden.
D000818:Animals; D001517:Coleoptera / Q000201:enzymology*; D011756:Diphosphates / Q000378:metabolism*; D049454:Firefly Luciferin / Q000378:metabolism*; D007700:Kinetics; D008027:Light; D008156:Luciferases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008163:Luminescent Measurements; D008956:Models, Chemical; D013237:Stereoisomerism; D013379:Substrate Specificity
D011756:Diphosphates; D049454:Firefly Luciferin; D008156:Luciferases