Abstract
Hemopexin (HPX), serving as scavenger and transporter of toxic plasma heme, has been postulated to play a key role in the homeostasis of NO. Here, kinetics of HPX-heme(II) nitrosylation and O2-mediated oxidation of HPX-heme(II)-NO are reported. NO reacts reversibly with HPX-heme(II) yielding HPX-heme(II)-NO, according to the minimum reaction scheme:{A formula is presented}values of kon, koff, and K (=kon/koff) are (6.3 ± 0.3) × 103 M-1 s-1, (9.1 ± 0.4) × 10-4 s-1, and (6.9 ± 0.6) × 106 M-1, respectively, at pH 7.0 and 10.0 °C. O2 reacts with HPX-heme(II)-NO yielding HPX-heme(III) and multiscripts(NO, mml:none(), mml:none(), 3, -), by means of the ferric heme-bound peroxynitrite intermediate (HPX-heme(III)-N(O)OO), according to the minimum reaction scheme:{A formula is presented}the backward reaction rate is negligible. Values of hon and l are (2.4 ± 0.3) × 101 M-1 s-1 and (1.4 ± 0.2) × 10-3 s-1, respectively, at pH 7.0 and 10.0 °C. The decay of HPX-heme(III)-N(O)OO (i.e., l) is rate limiting. The HPX-heme(III)-N(O)OO intermediate has been characterized by optical absorption spectroscopy in the Soret region (λmax = 409 nm and ε409 = 1.51 × 105 M-1 cm-1). These results, representing the first kinetic evidence for HPX-heme(II) nitrosylation and O2-mediated oxidation of HPX-heme(II)-NO, might be predictive of transient (pseudo-enzymatic) function(s) of heme carriers.
Original language | English |
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Pages (from-to) | 704-712 |
Number of pages | 9 |
Journal | Biochemical and Biophysical Research Communications |
Volume | 345 |
Issue number | 2 |
DOIs | |
Publication status | Published - Jun 30 2006 |
Keywords
- Ferrous hemopexin-heme nitrosylation
- Nitrate formation
- O-mediated oxidation of ferrous nitrosylated hemopexin-heme
- Rabbit hemopexin
ASJC Scopus subject areas
- Biochemistry
- Biophysics
- Molecular Biology