Inhibitory effect of organotin compounds on rat neuronal nitric oxide synthase through interaction with calmodulin.
Organotin compounds, triphenyltin (TPT), tributyltin, dibutyltin, and monobutyltin (MBT), showed potent inhibitory effects on both L-arginine oxidation to nitric oxide and L-citrulline, and cytochrome c reduction catalyzed by recombinant rat neuronal nitric oxide synthase (nNOS). The two inhibitory effects were almost parallel. MBT and TPT showed the highest inhibitory effects, followed by tributyltin and dibutyltin; TPT and MBT showed inhibition constant (IC(50)) values of around 10microM. Cytochrome c reduction activity was markedly decreased by removal of calmodulin (CaM) from the complete mixture, and the decrease was similar to the extent of inhibition by TPT and MBT. The inhibitory effect of MBT on the cytochrome c reducing activity was rapidly attenuated upon dilution of the inhibitor, and addition of a high concentration of CaM reactivated the cytochrome c reduction activity inhibited by MBT. However, other cofactors such as FAD, FMN or tetrahydrobiopterin had no such ability. The inhibitory effect of organotin compounds (100microM) on L-arginine oxidation of nNOS almost vanished when the amount of CaM was sufficiently increased (150-300microM). It was confirmed by CaM-agarose column chromatography that the dissociation of nNOS-CaM complex was induced by organotin compounds. These results indicate that organotin compounds disturb the interaction between CaM and nNOS, thereby inhibiting electron transfer from the reductase domain to cytochrome c and the oxygenase domain.
Graduate School of Biomedical Sciences, Hiroshima University, Kasumi 1-2-3, Minami-ku, Hiroshima 734-8551, Japan.
Koji
K
Ohashi
Shiro
S
Kominami
Takeshi
T
Yamazaki
Shigeru
S
Ohta
Shigeyuki
S
Kitamura
D000594:Amino Acid Oxidoreductases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D002147:Calmodulin / Q000378:metabolism*; D045304:Cytochromes c / Q000378:metabolism; D015394:Molecular Structure; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I; D009947:Organotin Compounds / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D010084:Oxidation-Reduction; D017434:Protein Structure, Tertiary; D051381:Rats; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
D002147:Calmodulin; D009947:Organotin Compounds; D011994:Recombinant Proteins; D045304:Cytochromes c; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; C496322:Nos1 protein, rat; D000594:Amino Acid Oxidoreductases; C040983:arginine oxidase