Vol. 302, Issue 2, 781-786, August 2002

The Activation of Neuronal Nitric-Oxide Synthase by Various Divalent Cations

John Weaver , Supatra Porasuphatana, Pei Tsai, Guan-Liang Cao, Theodore A. Budzichowski, Linda J. Roman and Gerald M. Rosen

Department of Chemistry, University of Maryland Baltimore County, Baltimore, Maryland (J.W., T.A.B.); Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland (J.W., P.T., G.-L.C., G.M.R.); Department of Toxicology, Faculty of Pharmaceutical Science, Khon Kaen University, Khon Kaen, Thailand (S.P.); Department of Biochemistry, the University of Texas Health Science Center at San Antonio, San Antonio, Texas (L.J.R.); Medical Biotechnology Center, University of Maryland Biotechnology Institute, Baltimore, Maryland (G.M.R.); and Center for Low-Frequency EPR for In Vivo Physiology, University of Maryland, Baltimore, Maryland (G.M.R.)

Nitric-oxide synthase (NOS; EC 1.14.13.39) catalyzes the oxidation of L-arginine to nitric oxide (NO^·) and L-citrulline via the intermediate N-hydroxy-L-arginine. Of the three distinct isoforms of NOS that have been characterized, the constitutive neuronal NOS (NOS I) generates NO^· associated with long-term potentiation (LTP) and early brain development. All of the NOS isoforms contain an N-terminal oxidase and a C-terminal reductase domain connected by a Ca²⁺/calmodulin binding region. To activate NOS I, Ca²⁺ has to bind to calmodulin, allowing electron transport through both domains. Calcium ions are tightly regulated in cells. However, a number of other metal ions that bind and activate calmodulin may also activate NOS I. One such metal ion may be Pb²⁺, which is associated with neurobehavioral and psychological alterations, including the inhibition of LTP. The effect of various divalent cations on NOS I activity was tested, and the results presented herein demonstrate that Pb²⁺ and Sr²⁺ can activate NOS I to a level similar to that found for Ca²⁺. Finally, there is a synergy between Pb²⁺ and Ca²⁺ resulting in maximal activation of NOS I using minimal concentrations of both metal ions.