Allosteric Control of Oxygen Binding by Haemoglobin During Embryonic Development in the Crocodile Crocodylus Porosus: The Role of Red Cell Organic Phosphates and Carbon Dioxide

Abstract

The P50 of whole blood [30°C, PCO2=2.08 kPa (15.6 mmHg)] decreases during embryonic development from approximately 6.7 kPa (50 mmHg) at 15 days to about half this value at hatching (86 days), paralleling a decrease in ATP from 100 to 5–10 micromole g-1 Hb. There is also a progressive changeover from embryonic to adult haemoglobin (HbA). A pulse of 2,3- diphosphoglycerate (2,3-DPG) (18 micromole g-1 Hb) occurs late in embryonic life. It has no effect on whole-blood oxygen-affinity and falls rapidly at hatching to values typical of post-hatchling crocodilians in general (<1.0 micromole g-1 Hb). ATP has a marked effect on the oxygen affinity of embryonic haemoglobin (HbE) but not on HbA. 2,3-DPG has only very small effects on the oxygen affinities of HbE and HbA. CO2 has a small effect on the oxygen affinity of HbE but a marked effect on that of HbA. Values of PO2 measured in the chorio-allantoic artery [2.9 kPa (22 mmHg)] and vein [5.9 kPa (52 mmHg)] imply an increase in saturation from approximately 30 % to more than 80 %. Neither whole-blood oxygen-affinity nor ATP level was altered in response to an experimental 7-day exposure to low ambient oxygen levels [10.7 kPa (80 mmHg)]. The results do not lend themselves easily to the pan-selectionist paradigm in which all physiological traits are viewed as being adaptive.

Changes in hemoglobin function and isoform expression during embryonic development in the American alligator, Alligator mississippiensis

“…By contrast, studies of embryonic saltwater crocodiles (Crocodylus porosus) (37) reported a progressive left-shift of the O 2 equilibrium curves of whole blood during development. Assuming that crocodiles and alligators are comparable in their embryonic development, the apparent discrepancy between our results (obtained with ATP-free hemolysate) and those of Grigg et al (37) may be explained by developmental changes in erythrocytic ATP concentration. High ATP at early development would shift whole blood O 2 equilibrium curves to the right, especially since ATP-sensitive HbI (Fig.…”

“…5, C and D). The progressive increase in the Hb-CO 2 sensitivity during development was also observed in crocodile embryos (37).…”

“…5, A and B) is highly abundant at these stages (Fig. 3A), whereas the use of CO 2 in whole blood experiments (37) mostly right shifted the O 2 equilibrium curves at later development. We note that the progressive shift of purified Hb isoforms from high-to low-O 2 affinity during alligator development (Fig.…”

Changes in hemoglobin function and isoform expression during embryonic development in the American alligator, Alligator mississippiensis

“…By contrast, studies of embryonic saltwater crocodiles (Crocodylus porosus) (37) reported a progressive left-shift of the O 2 equilibrium curves of whole blood during development. Assuming that crocodiles and alligators are comparable in their embryonic development, the apparent discrepancy between our results (obtained with ATP-free hemolysate) and those of Grigg et al (37) may be explained by developmental changes in erythrocytic ATP concentration. High ATP at early development would shift whole blood O 2 equilibrium curves to the right, especially since ATP-sensitive HbI (Fig.…”

“…5, C and D). The progressive increase in the Hb-CO 2 sensitivity during development was also observed in crocodile embryos (37).…”

“…5, A and B) is highly abundant at these stages (Fig. 3A), whereas the use of CO 2 in whole blood experiments (37) mostly right shifted the O 2 equilibrium curves at later development. We note that the progressive shift of purified Hb isoforms from high-to low-O 2 affinity during alligator development (Fig.…”

Vertebrate Hemoglobins

“…Further, embryonic red cells contain appreciable quantities of ATP, which decline during embryonic development. (Also, similar to that seen in turtle and avian embryos [22,301,594], there exists a temporary pulse of 2,3-DPG in these embryonic red cells late in embryonic life [242]. )…”

“…To this end, some embryos and fetuses use ontogenetically Baldwin (594) speculate that the presence of elevated levels of organic phosphates as well as an embryonic hemoglobin sensitive to these phosphates in the hatchling may represent an adaptation to hypoxia during development in the nest rather than to the activity of dispersal after hatch. As mentioned previously (see under Sensitivity to Bicarbonate), the embryonic hemoglobin of the crocodile is functionally distinct from that of the adult by being relatively insensitive to carbon dioxide and by being sensitive to allosteric regulation by ATP (242). The blood oxygen affinity of the embryo decreases during embryonic life and parallels a decrease in red cell ATP levels.…”

Changes in hemoglobin function and isoform expression during embryonic development in the American alligator, Alligator mississippiensis

“…By contrast, studies of embryonic saltwater crocodiles (Crocodylus porosus) (37) reported a progressive left-shift of the O 2 equilibrium curves of whole blood during development. Assuming that crocodiles and alligators are comparable in their embryonic development, the apparent discrepancy between our results (obtained with ATP-free hemolysate) and those of Grigg et al (37) may be explained by developmental changes in erythrocytic ATP concentration. High ATP at early development would shift whole blood O 2 equilibrium curves to the right, especially since ATP-sensitive HbI (Fig.…”

“…5, C and D). The progressive increase in the Hb-CO 2 sensitivity during development was also observed in crocodile embryos (37).…”

“…5, A and B) is highly abundant at these stages (Fig. 3A), whereas the use of CO 2 in whole blood experiments (37) mostly right shifted the O 2 equilibrium curves at later development. We note that the progressive shift of purified Hb isoforms from high-to low-O 2 affinity during alligator development (Fig.…”

Vertebrate Hemoglobins

“…Further, embryonic red cells contain appreciable quantities of ATP, which decline during embryonic development. (Also, similar to that seen in turtle and avian embryos [22,301,594], there exists a temporary pulse of 2,3-DPG in these embryonic red cells late in embryonic life [242]. )…”

“…To this end, some embryos and fetuses use ontogenetically Baldwin (594) speculate that the presence of elevated levels of organic phosphates as well as an embryonic hemoglobin sensitive to these phosphates in the hatchling may represent an adaptation to hypoxia during development in the nest rather than to the activity of dispersal after hatch. As mentioned previously (see under Sensitivity to Bicarbonate), the embryonic hemoglobin of the crocodile is functionally distinct from that of the adult by being relatively insensitive to carbon dioxide and by being sensitive to allosteric regulation by ATP (242). The blood oxygen affinity of the embryo decreases during embryonic life and parallels a decrease in red cell ATP levels.…”

Changes in hemoglobin function and isoform expression during embryonic development in the American alligator, Alligator mississippiensis

“…By contrast, studies of embryonic saltwater crocodiles (Crocodylus porosus) (37) reported a progressive left-shift of the O 2 equilibrium curves of whole blood during development. Assuming that crocodiles and alligators are comparable in their embryonic development, the apparent discrepancy between our results (obtained with ATP-free hemolysate) and those of Grigg et al (37) may be explained by developmental changes in erythrocytic ATP concentration. High ATP at early development would shift whole blood O 2 equilibrium curves to the right, especially since ATP-sensitive HbI (Fig.…”

“…5, C and D). The progressive increase in the Hb-CO 2 sensitivity during development was also observed in crocodile embryos (37).…”

“…5, A and B) is highly abundant at these stages (Fig. 3A), whereas the use of CO 2 in whole blood experiments (37) mostly right shifted the O 2 equilibrium curves at later development. We note that the progressive shift of purified Hb isoforms from high-to low-O 2 affinity during alligator development (Fig.…”

Vertebrate Hemoglobins

“…Further, embryonic red cells contain appreciable quantities of ATP, which decline during embryonic development. (Also, similar to that seen in turtle and avian embryos [22,301,594], there exists a temporary pulse of 2,3-DPG in these embryonic red cells late in embryonic life [242]. )…”

“…To this end, some embryos and fetuses use ontogenetically Baldwin (594) speculate that the presence of elevated levels of organic phosphates as well as an embryonic hemoglobin sensitive to these phosphates in the hatchling may represent an adaptation to hypoxia during development in the nest rather than to the activity of dispersal after hatch. As mentioned previously (see under Sensitivity to Bicarbonate), the embryonic hemoglobin of the crocodile is functionally distinct from that of the adult by being relatively insensitive to carbon dioxide and by being sensitive to allosteric regulation by ATP (242). The blood oxygen affinity of the embryo decreases during embryonic life and parallels a decrease in red cell ATP levels.…”