Thermodynamic analysis of L-arginine and N omega-hydroxy-L-arginine binding to nitric oxide synthase.
Isothermal titration calorimetry has been used to determine thermodynamic parameters of substrate binding to the oxygenase domain of neuronal nitric oxide synthase (nNOS(oxy)) in the presence of the cofactor tetrahydrobiopterin. The intermediate N(omega)-hydroxy-L-arginine (NHA) has a larger affinity than L-Arginine (L-Arg) for nNOS(oxy), with K(d)=0.4+/-0.1 microM and 1.7+/-0.3 microM at 25 degrees C, respectively. nNOS(oxy) binds NHA and L-Arg with DeltaH -4.1+/-0.2 and -1.0+/-0.1 kcal/mol and DeltaS=15 and 23 cal/Kmol respectively. NHA binding is more exothermic probably due to formation of an extra hydrogen bond in the active site compared to L-Arg. The changes in heat capacity (DeltaC(p)) are relatively small for binding of both NHA and L-Arg (-53+/-18 and -95+/-23 cal/L mol, respectively), which indicates that hydrophobic interactions contribute little to binding.
Zakariassen
Henrik
H
Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, P.O. Box 5003, N-1432 Aas, Norway.
Cederkvist
F Henning
FH
Harbitz
Espen
E
Shimizu
Toru
T
Lange
Reinhard
R
Mayer
Bernd
B
Gorren
Antonius C F
AC
Andersson
K Kristoffer
KK
Sørlie
Morten
M
D001120:Arginine / Q000031:analogs & derivatives* / Q000378:metabolism*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D019277:Entropy; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D013696:Temperature
C068309:N(omega)-hydroxyarginine; D001120:Arginine; D019001:Nitric Oxide Synthase