TY - JOUR
T1 - Calmodulin-dependent regulation of inducible and neuronal nitric-oxide synthase
AU - Lee, Shiow Ju
AU - Stull, James T.
PY - 1998/10/16
Y1 - 1998/10/16
N2 - Neuronal and endothelial nitric-oxide synthases depend upon Ca2+/calmodulin for activation, whereas the activity of the inducible nitric-oxide synthase is Ca2+-independent, presumably due to tightly bound calmodulin. To study these different mechanisms, a series of chimeras derived from neuronal and inducible nitric-oxide synthases were analyzed. Chimeras containing only the oxygenase domain, calmodulin-binding region, or reductase domain of inducible nitric-oxide synthase did not confer significant Ca2+- independent activity. However, each chimera was more sensitive to Ca2+ than the neuronal isoform. The calmodulin-binding region of inducible nitric- oxide synthase with either its oxygenase or reductase domains resulted in significant, but not total, Ca2+-independent activity. Co- immunoprecipitation experiments showed no calmodulin associated with the former chimera in the absence of Ca2+. Trifluoperazine also inhibited this chimera in the absence of Ca2+. The combined interactions of calmodulin bound to inducible nitric-oxide synthase calmodulin-binding region with the oxygenase domain may be weaker than with the reductase domain. Thus, Ca2+- independent activity of inducible nitric-oxide synthase appears to result from the concerted interactions of calmodulin with both the oxygenase and reductase domains in addition to the canonical calmodulin-binding region. The neuronal isoform is not regulated by a unique autoinhibitory element in its reductase domain.
AB - Neuronal and endothelial nitric-oxide synthases depend upon Ca2+/calmodulin for activation, whereas the activity of the inducible nitric-oxide synthase is Ca2+-independent, presumably due to tightly bound calmodulin. To study these different mechanisms, a series of chimeras derived from neuronal and inducible nitric-oxide synthases were analyzed. Chimeras containing only the oxygenase domain, calmodulin-binding region, or reductase domain of inducible nitric-oxide synthase did not confer significant Ca2+- independent activity. However, each chimera was more sensitive to Ca2+ than the neuronal isoform. The calmodulin-binding region of inducible nitric- oxide synthase with either its oxygenase or reductase domains resulted in significant, but not total, Ca2+-independent activity. Co- immunoprecipitation experiments showed no calmodulin associated with the former chimera in the absence of Ca2+. Trifluoperazine also inhibited this chimera in the absence of Ca2+. The combined interactions of calmodulin bound to inducible nitric-oxide synthase calmodulin-binding region with the oxygenase domain may be weaker than with the reductase domain. Thus, Ca2+- independent activity of inducible nitric-oxide synthase appears to result from the concerted interactions of calmodulin with both the oxygenase and reductase domains in addition to the canonical calmodulin-binding region. The neuronal isoform is not regulated by a unique autoinhibitory element in its reductase domain.
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U2 - 10.1074/jbc.273.42.27430
DO - 10.1074/jbc.273.42.27430
M3 - Article
C2 - 9765272
AN - SCOPUS:0032538572
SN - 0021-9258
VL - 273
SP - 27430
EP - 27437
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 42
ER -