RT Journal Article
SR Electronic
T1 Structure-Related Inhibition of Calmodulin-Dependent Neuronal Nitric-Oxide Synthase Activity by Melatonin and Synthetic Kynurenines
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 967
OP 975
DO 10.1124/mol.58.5.967
VO 58
IS 5
A1 León, Josefa
A1 Macías, Manuel
A1 Escames, Germaine
A1 Camacho, Encarna
A1 Khaldy, Huda
A1 Martín, Miguel
A1 Espinosa, Antonio
A1 Gallo, Miguel A.
A1 Acuña-Castroviejo, Darío
YR 2000
UL http://molpharm.aspetjournals.org/content/58/5/967.abstract
AB We recently described that melatonin and some kynurenines modulate theN-methyl-d-aspartate-dependent excitatory response in rat striatal neurons, an effect that could be related to their inhibition of nNOS. In this report, we studied the effect of melatonin and these kynurenines on nNOS activity in both rat striatal homogenate and purified rat brain nNOS. In homogenates of rat striatum, melatonin inhibits nNOS activity, whereas synthetic kynurenines act in a structure-related manner. Kynurenines carrying an NH2group in their benzenic ring (NH2-kynurenines) inhibit nNOS activity more strongly than melatonin itself. However, kynurenines lacking the NH2 group or with this group blocked do not affect enzyme activity. Kinetic analysis shows that melatonin and NH2-kynurenines behave as noncompetitive inhibitors of nNOS. Using purified rat brain nNOS, we show that the inhibitory effect of melatonin and NH2-kynurenines on the enzyme activity diminishes with increasing amounts of calmodulin in the incubation medium. However, changes in other nNOS cofactors such as FAD or H4-biopterin, do not modify the drugs' response. These data suggest that calmodulin may be involved in the nNOS inhibition by these compounds. Studies with urea-polyacrylamide gel electrophoresis further support an interaction between melatonin and NH2-kynurenines, but not kynurenines lacking the NH2 group, with Ca2+-calmodulin yielding Ca2+-calmodulin-drug complexes that prevent nNOS activation. The results show that calmodulin is a target involved in the intracellular effects of melatonin and some melatonin-related kynurenines that may account, at least in part, for the neuroprotective properties of these compounds.