PT - JOURNAL ARTICLE AU - Jennifer L. Vuletich AU - Ezra R. Lowe AU - Suree Jianmongkol AU - Yasuhiko Kamada AU - Ute M. Kent AU - Andrew T. Bender AU - Damon R. Demady AU - Paul F. Hollenberg AU - Yoichi Osawa TI - Alteration of the Heme Prosthetic Group of Neuronal Nitric-Oxide Synthase during Inactivation by<em>N</em> <sup>G</sup>-Amino-<span class="sc">l</span>-arginine in Vitro and in Vivo AID - 10.1124/mol.62.1.110 DP - 2002 Jul 01 TA - Molecular Pharmacology PG - 110--118 VI - 62 IP - 1 4099 - http://molpharm.aspetjournals.org/content/62/1/110.short 4100 - http://molpharm.aspetjournals.org/content/62/1/110.full SO - Mol Pharmacol2002 Jul 01; 62 AB - It is established thatN G-amino-l-arginine (NAA) is a metabolism-based inactivator of all three major nitric-oxide synthase (NOS) isoforms. The mechanism by which this inactivation occurs, however, is not well understood. In the current study, we discovered that inactivation of the neuronal isoform of NOS (nNOS) by NAA in vitro results in covalent alteration of the heme prosthetic group, in part, to products that contain an intact porphyrin ring and are either dissociable from or irreversibly bound to the protein. The alteration of the heme is concomitant with the loss of nNOS activity. Studies with nNOS containing a 14C-labeled prosthetic heme moiety indicate that the major dissociable product and the irreversibly bound heme adduct account for 21 and 28%, respectively, of the heme that is altered. Mass spectral analysis of the major dissociable product gave a molecular ion ofm/z 775.3 that is consistent with the mass of an adduct of heme and NAA minus a hydrazine group. Peptide mapping of the irreversibly bound heme adduct indicates that the heme is bound to a residue in the oxygenase domain of nNOS. We show for the first time that metabolism-based inactivation of nNOS occurs in vivo as highly similar heme products are formed. Because inactivation and alteration may trigger ubiquitination and proteasomal degradation of nNOS, NAA may be a useful biochemical tool for the study of these basic regulatory processes.