Biology Reference
In-Depth Information
conformations (penta- vs. hexacoordinated haem) with different redox poten-
tials. This behaviour may be considered as an ancestral mechanism for mod-
ulating a conformational switch between two functional species (
Russo
et al., 2013
).
Ph
-2/2HbO is quickly oxidised in the presence of O
2
, probably due to
the superoxide character of the haem-Fe-O
2
adduct, affected by the pres-
ence of the surrounding hydrogen-bond donor residues (
Milani et al.,
2001, 2003
).
The O
2
affinity, poorly affected by competition with Tyr, is about 1 Torr
at 8
C, pH 7.0 (
Table 8.4
). The O
2
affinity of
Ph
-2/2HbO is compatible
with the
in vivo
conditions (
Fig. 8.7
A), considering that the
Ph
TAC125 bac-
terial metabolism must cope with high O
2
concentration and high-salinity
conditions at low temperature. However, Mb-like functions do not seem
to be possible for
Ph
-2/2HbO, requiring a still unknown efficient reducing
system, and a local high globin concentration (
Russo et al., 2013
).
Figure 8.7 Some postulated functions of Ph-2/2HbO. (A) O
2
carrier even though this
function requires the presence of a still unknown coupled reductase systemfor high turn-
over reaction; (B) Ph-2/2HbO may convert NO to nitrate and (C) nitrite to NO; (D) it
may detoxify RNS and (E) ROS; (F) itmay function as electron transfer coupled to an accep-
tor molecule. The model of Ph-2/2HbO was kindly provided by L. Boechi.
