Oxygen binding to Arabidopsis thaliana AHb2 nonsymbiotic hemoglobin: Evidence for a role in oxygen transport

Abstract

Nonsymbiotic hemoglobins AHb1 and AHb2 discovered in Arabidopsis thaliana are likely to carry out distinct physiological roles, in consideration of their differences in sequence, structure, expression pattern, and tissue localization. Despite a relatively fast autoxidation in the presence of O2, we were able to collect O2-binding curves for AHb2 in the presence of a reduction enzymatic system. AHb2 binds O2 noncooperatively with a p50 of 0.021 ± 0.003 Torr, a value consistent with a recently proposed role in O2 transport. The analysis of the internal cavities derived from the structures sampled in molecular dynamics simulations confirms strong differences with AHb1, proposed to work as a NO deoxygenase in vivo. Overall, our results are consistent with a role for AHb2 as an oxygen carrier, as recently proposed on the basis of experiments on AHb2-overexpressing mutants of A. thaliana. Copyright © 2011 Wiley Periodicals, Inc.