Abstract
This study was designed to evaluate thein vitro effects of transition heavy metal cations on activity of constitutive isoform of nitric oxide synthase (cNOS) in rat brain. NOS activity was determined in the cytosolic fractions of rat cerebral hemispheres by conversion of3H-L-arginine to3H-L-citrulline. Different concentrations of mercury (Hg2+), nickel (Ni2+), manganese (Mn2+), zinc (Zn2+), cadmium (Cd2+), lead (Pb2+) and calcium (Ca2+) were tested on NOS activity. While all the cations caused inhibition, there were differences in the apparent inhibition constants (Ki) among the cations. With the exception of calcium ion no other cation required preincubation with the enzyme preparation. These results indicate that while calcium ion modulate cNOS activity at regulatory site(s), inhibitory influence of toxic heavy metal cations may be exerted on the catalytic site(s) either by direct binding to it or by interfering with the electron transfer during catalysis.
Similar content being viewed by others
References
Nathan C: Nitric oxide as a secretory product of mammalian cells. FASEB J 6: 3051–3064, 1992
Dawson TM, Bredt DS, Foktuhi M, Hwang PM, Snyder SH: Nitric oxide synthase and neuronal diaphorase are identical in brain and peripheral tissues. Proc Nat Acad Sci USA 88: 7797–7801, 1991
Klatt P, Heinzel B, John M, Kastner M, Bohme E, Mayer B: Ca2+/calmodulin-dependent cytochrome C reductase activity of brain nitric oxide synthase. J Biol Chem 267: 11374–11378, 1992
White KA, Marletta MA: Nitric oxide synthase is a cytochrome P-450 type hemoprotein. Biochem 31: 6627–6631, 1992
Kwon NS, Nathan CF, Stuehr DJ: Reduced biopterine as a cofactor in the generation of nitrogen oxides by murine macrophages. J Biol Chem 264: 20496–20501, 1989
Mittal CK: Nitric oxide synthase: Involvement of oxygen radicals in conversion of L-arginine to nitric oxide. Biochem Biophys Res Commun 193: 126–132, 1993
Mittal CK, Jadhav AL: Calcium-dependent inhibition of constitutive nitric oxide synthase. Biochem Biophys Res Commun 203: 8–15, 1994
Pollock JS, Forstermann U, Mitchell JA, Warner TD, Schmidt HBIW, Nakane M, Murad F: Purification and characterization of particulate endothelium derived relaxing factor synthase from cultured and native bovine aortic endothelial cells. Proc Nat Acad Sci USA 88: 10480–10484, 1991
Pufahl RA, Marletta MA: Oxidation of NG-hydroxy-L-arginine by nitric oxide synthase: Evidence for the involvement of the heme in catalysis. Biochem Biophys Res Commun 193: 963–970, 1993
Joshi P, Desaiah D: Inhibition of nitric oxide synthase activity in rat brain by metals. The Toxicologist 14 (1): 198, 1994
Mittal CK, Houston DE: Differential modulatory effects of heavy metal toxicants on constitutive nitric oxide synthase. The Toxicologist 15: 10 (1995)
Fong K, McCay PB, Poyre JL, Keele BB, Misra HP: Evidence that peroxidation of Iysosomal membranes is initiated by hydroxyl free radicals produced during flavin enzyme activity. J Biol Chem 248: 7792–7797, 1973
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Mittal, C.K., Harrell, W.B. & Mehta, C.S. Interaction of heavy metal toxicants with brain constitutive nitric oxide synthase. Mol Cell Biochem 149, 263–265 (1995). https://doi.org/10.1007/BF01076586
Issue Date:
DOI: https://doi.org/10.1007/BF01076586