The role of tetrahydrobiopterin in the regulation of neuronal nitric-oxide synthase-generated superoxide.
Tetrahydrobiopterin (H(4)B) is a critical element in the nitric-oxide synthase (NOS) metabolism of l-arginine to l-citrulline and NO(.). It has been hypothesized that in the absence of or under nonsaturating levels of L-arginine where O(2) reduction is the primary outcome of NOS activation, H(4)B promotes the generation of H(2)O(2) at the expense of O(2)(-.). The experiments were designed to test this hypothesis. To test this theory, two different enzyme preparations, H(4)B-bound NOS I and H(4)B-free NOS I, were used. Initial rates of NADPH turnover and O(2) utilization were found to be considerably greater in the H(4)B-bound NOS I preparation than in the H(4)B-free NOS I preparation. In contrast, the initial generation of O(2)(-.) from the H(4)B-free NOS I preparation was found to be substantially greater than that measured using the H(4)B-bound NOS I preparation. Finally, by spin trapping nearly all of the NOS I produced O(2)(-.), we found that the initial rate of H(2)O(2) production by H(4)B-bound NOS I was considerably greater than that for H(4)B-free NOS I.
Rosen
Gerald M
GM
Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, 725 West Lombard Street, Baltimore, MD 21201, USA. grosen@umaryland.edu
Tsai
Pei
P
Weaver
John
J
Porasuphatana
Supatra
S
Roman
Linda J
LJ
Starkov
Anatoly A
AA
Fiskum
Gary
G
Pou
Sovitj
S
D001708:Biopterins / Q000031:analogs & derivatives* / Q000502:physiology*; D006861:Hydrogen Peroxide / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism / Q000502:physiology*; D052248:Nitric Oxide Synthase Type I; D010100:Oxygen / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism*
D013481:Superoxides; D001708:Biopterins; D009249:NADP; D006861:Hydrogen Peroxide; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; C003402:sapropterin; D010100:Oxygen