Article,
Aminoguanidine-mediated inactivation and alteration of neuronal nitric-oxide synthase.
J Biol Chem, 275 (18): 13370--13376 (May 2000)
Abstract
It is established that aminoguanidine (AG) is a metabolism-based inactivator
of the three major isoforms of nitric-oxide synthase. AG is thought
to be of potential use in diseases, such as diabetes, where pathological
overproduction of NO is implicated. We show here that during the
inactivation of neuronal nitric-oxide synthase (nNOS) by AG that
the prosthetic heme is altered, in part, to dissociable and protein-bound
adducts. The protein-bound heme adduct is the result of cross-linking
of the heme to residues in the oxygenase domain of nNOS. The dissociable
heme product is unstable and reverts back to heme upon isolation.
The alteration of the heme is concomitant with the loss in the ability
to form the ferrous-CO complex of nNOS and accounts for at least
two-thirds of the activity loss. Studies with (14)CAG indicate
that alteration of the protein, in part on the reductase domain
of nNOS, also occurs but at low levels. Thus, heme alteration appears
to be the major cause of nNOS inactivation. The elucidation of the
mechanism of inactivation of nNOS will likely lead to a better understanding
of the in vivo effects of NOS inhibitors such as AG.
