title: Ca2+-independent activity of nitric oxide synthase.
abstract: Ca2+-independent forms of nitric-oxide synthase have significant activity when the endogenous calmodulin subunit is Ca2+ free. Further activation is seen when Ca2+ is added. We have examined the activation of a Ca2+-independent nitric-oxide synthase variant and its two point mutants that are more dependent on Ca2+ for activation using mutant calmodulins containing non-functional Ca2+-binding sites. These studies provide evidence that the Ca2+-independent activity of these enzymes can be exerted through specific adapted interactions between the enzyme and the Ca2+-binding site 2 of calmodulin. Further, the results suggest that EGTA-sensitive metals other than Ca2+ complexed to calmodulin may be involved in maximal activation of these nitric-oxide synthase variants.
authors.affiliation: Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9040, USA. slee@resgen.com
authors.forename: S J
authors.initials: SJ
authors.lastname: Lee
authors.forename: K
authors.initials: K
authors.lastname: Beckingham
authors.forename: J T
authors.initials: JT
authors.lastname: Stull
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000502:physiology; D019556:COS Cells; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000235:genetics / Q000378:metabolism; D002413:Cations, Divalent / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000235:genetics / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D017354:Point Mutation; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D002147:Calmodulin; D002413:Cations, Divalent; D002614:Chelating Agents; D011993:Recombinant Fusion Proteins; D004533:Egtazic Acid; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D002118:Calcium