346
G. di Prisco
These remarkable characteristics are shared by the Hbs of A. orianae
and P. scotti. It is astonishing that Hbs of far-from-primitive
Artedidraconidae are displaying functional properties typical of primitive
organisms. If extreme conditions have driven evolution towards low
metabolism and decreased dependence on Hb-mediated oxygen transport,
this functional behavior may well be consistent with the less critical
physiological role of Hb. The lack of cooperative oxygen binding is even
more astonishing in the light of the high sequence identity of these Hbs (to
be consequently regarded as "modem") with the "normal" major Hbs of
the other notothenioids, and raises interesting questions on the mode of
function of multi subunit molecules.
N onAntarctic N otothenioidei
Morphology [27,28] and karyology [29] indicate Bovichtidae as the most
primitive notothenioid family [30-32], which comprises eleven species,
living in temperate waters except Bovichtus elongatus (Antarctic
Peninsula).
A recently proposed classification [33] separates the new family
Pseudaphritidae from Bovichtidae.
The bovichtid (or pseudaphritid) Pseudaphritis urvillii, common in
estuaries and the lower portion of Australian rivers, is considered a relict
species. No information was available on the Hb system of this primitive
family.
Like most notothenioids, P. urvillii has a major (Hb 1) and a minor
component (Hb 2). Hb 1 has a strong Bohr effect; the Root effect is ATPinduced [34-36].
Although the Hb multiplicity closely resembles that of sedentary
Antarctic notothenioids, the oxygen affinity of Hb 1 is much higher; in
fact, 10gPso stays below zero in the pH range 8.0-7.0. This feature can be
ascribed to the widely different constraints arising from the habitat of this
nonAntarctic species, and is likely to be reflected in changes in the primary
structure. We have indeed found two substitutions which may alter the
geometry of the invariantly hydrophobic heme pocket: in a87(F) and a
92(FG3) Glu and Met replace Leu. Glu a87(F) is found only in this
species; interestingly, all Antarctic Notothenioidei have GIn, whose codon
differs from that of Glu by a single base change at the first position.
Although P. urvillii has never developed cold adaptation, the globin
amino acid sequences reveal high identity with those of the other
notothenioids.
G. di Prisco
These remarkable characteristics are shared by the Hbs of A. orianae
and P. scotti. It is astonishing that Hbs of far-from-primitive
Artedidraconidae are displaying functional properties typical of primitive
organisms. If extreme conditions have driven evolution towards low
metabolism and decreased dependence on Hb-mediated oxygen transport,
this functional behavior may well be consistent with the less critical
physiological role of Hb. The lack of cooperative oxygen binding is even
more astonishing in the light of the high sequence identity of these Hbs (to
be consequently regarded as "modem") with the "normal" major Hbs of
the other notothenioids, and raises interesting questions on the mode of
function of multi subunit molecules.
N onAntarctic N otothenioidei
Morphology [27,28] and karyology [29] indicate Bovichtidae as the most
primitive notothenioid family [30-32], which comprises eleven species,
living in temperate waters except Bovichtus elongatus (Antarctic
Peninsula).
A recently proposed classification [33] separates the new family
Pseudaphritidae from Bovichtidae.
The bovichtid (or pseudaphritid) Pseudaphritis urvillii, common in
estuaries and the lower portion of Australian rivers, is considered a relict
species. No information was available on the Hb system of this primitive
family.
Like most notothenioids, P. urvillii has a major (Hb 1) and a minor
component (Hb 2). Hb 1 has a strong Bohr effect; the Root effect is ATPinduced [34-36].
Although the Hb multiplicity closely resembles that of sedentary
Antarctic notothenioids, the oxygen affinity of Hb 1 is much higher; in
fact, 10gPso stays below zero in the pH range 8.0-7.0. This feature can be
ascribed to the widely different constraints arising from the habitat of this
nonAntarctic species, and is likely to be reflected in changes in the primary
structure. We have indeed found two substitutions which may alter the
geometry of the invariantly hydrophobic heme pocket: in a87(F) and a
92(FG3) Glu and Met replace Leu. Glu a87(F) is found only in this
species; interestingly, all Antarctic Notothenioidei have GIn, whose codon
differs from that of Glu by a single base change at the first position.
Although P. urvillii has never developed cold adaptation, the globin
amino acid sequences reveal high identity with those of the other
notothenioids.