Oxygen and nitric oxide rebinding kinetics in nonsymbiotic hemoglobin AHb1 from Arabidopsis thaliana.
Type 1 nonsymbiotic hemoglobin from Arabidopsis thaliana (AHb1) shows a partial bis-histidyl hexacoordination but can reversibly bind diatomic ligands. The physiological function is still unclear, but the high oxygen affinity rules out a function related to O2 sensing, carrying, or storing. To gain insight into its possible functional roles, we have investigated its O2 and NO rebinding kinetics after laser flash photolysis. The rate constants of the rebinding from the primary docking site for both O2 and NO are higher than CO, with lower photolysis yields. Moreover, the amplitude of the geminate phase increases and, as for CO, the numerical analysis of the experimental curves suggests the existence of an internal pathway leading, with high rate, to an additional docking site. However, the accessibility to this site seems to be strongly ligand-dependent, being lower for O2 and higher for NO.
Dipartimento di Fisica, Università degli Studi di Parma, Parma, Italy. stefania.abbruzzetti@fis.unipr.it
Stefania
S
Abbruzzetti
Serena
S
Faggiano
Francesca
F
Spyrakis
Stefano
S
Bruno
Andrea
A
Mozzarelli
Alessandra
A
Astegno
Paola
P
Dominici
Cristiano
C
Viappiani
D017360:Arabidopsis / Q000737:chemistry* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry*; D002248:Carbon Monoxide / Q000737:chemistry; D006454:Hemoglobins / Q000737:chemistry*; D007700:Kinetics; D007834:Lasers; D008024:Ligands; D008958:Models, Molecular; D009569:Nitric Oxide / Q000737:chemistry*; D009716:Numerical Analysis, Computer-Assisted; D010100:Oxygen / Q000737:chemistry*; D010782:Photolysis; D011485:Protein Binding; D011487:Protein Conformation; D011994:Recombinant Proteins
C470347:AHB1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D006454:Hemoglobins; D008024:Ligands; D011994:Recombinant Proteins; D009569:Nitric Oxide; D002248:Carbon Monoxide; D010100:Oxygen