Oxygen metabolism by endothelial nitric-oxide synthase.
Nitric-oxide synthase (NOS) catalyzes both coupled and uncoupled reactions that generate nitric oxide and reactive oxygen species. Oxygen is often the overlooked substrate, and the oxygen metabolism catalyzed by NOS has been poorly defined. In this paper we focus on the oxygen stoichiometry and effects of substrate/cofactor binding on the endothelial NOS isoform (eNOS). In the presence of both L-arginine and tetrahydrobiopterin, eNOS is highly coupled (>90%), and the measured stoichiometry of O(2)/NADPH is very close to the theoretical value. We report for the first time that the presence of L-arginine stimulates oxygen uptake by eNOS. The fact that nonhydrolyzable L-arginine analogs are not stimulatory indicates that the occurrence of the coupled reaction, rather than the accelerated uncoupled reaction, is responsible for the L-arginine-dependent stimulation. The presence of 5,6,7,8-tetrahydrobiopterin quenched the uncoupled reactions and resulted in much less reactive oxygen species formation, whereas the presence of redox-incompetent 7,8-dihydrobiopterin demonstrates little quenching effect. These results reveal different mechanisms for oxygen metabolism for eNOS as opposed to nNOS and, perhaps, partially explain their functional differences.
Gao
Ying Tong
YT
Department of Biochemistry, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229-3900.
Roman
Linda J
LJ
Department of Biochemistry, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229-3900.
Martásek
Pavel
P
Department of Pediatrics, Charles University School of Medicine I, 128 08 Prague, Czech Republic.
Panda
Satya Prakash
SP
Department of Biochemistry, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229-3900.
Ishimura
Yuzuru
Y
Department of Biochemistry and Integrated Biology, School of Medicine, Keio University, Tokyo 160-8582, Japan.
Masters
Bettie Sue S
BSS
Department of Biochemistry, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229-3900. Electronic address: masters@uthscsa.edu.
D000818:Animals; D001120:Arginine / Q000737:chemistry* / Q000378:metabolism; D001708:Biopterins / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D002384:Catalysis; D006801:Humans; D009569:Nitric Oxide / Q000737:chemistry / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I / Q000737:chemistry / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000737:chemistry* / Q000378:metabolism; D009602:Nitrosamines / Q000737:chemistry / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000737:chemistry* / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
D009602:Nitrosamines; D017382:Reactive Oxygen Species; D011994:Recombinant Proteins; D001708:Biopterins; D009569:Nitric Oxide; C041199:N-nitrosoallyl-2,3-dihydroxypropylamine; D001120:Arginine; C496314:NOS3 protein, human; D052248:Nitric Oxide Synthase Type I; D052250:Nitric Oxide Synthase Type III; C003402:sapropterin; D010100:Oxygen