New insights into the allosteric effects of CO2 and bicarbonate on crocodilian hemoglobin
| Autor: | Chandrasekhar Natarajan, Jay F. Storz, Naim M. Bautista, Tobias Wang, Angela Fago, Hans Malte |
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| Rok vydání: | 2021 |
| Předmět: |
Physiology
Direct evidence 030310 physiology Bicarbonate Alligator Allosteric regulation Aquatic Science 03 medical and health sciences chemistry.chemical_compound Hemoglobins Allosteric Regulation biology.animal Animals Adaptation Molecular Biology Bicarbonate binding Ecology Evolution Behavior and Systematics 030304 developmental biology 0303 health sciences Alligators and Crocodiles biology myr Carbon Dioxide Oxygen Bicarbonates Blood Carbon dioxide chemistry Biochemistry Insect Science Animal Science and Zoology Hemoglobin Digestion Research Article |
| Zdroj: | J Exp Biol Bautista, N M, Malte, H, Natarajan, C, Wang, T, Storz, J F & Fago, A 2021, ' New insights into the allosteric effects of CO 2 and Bicarbonate on Crocodilian Hemoglobin ', Journal of Experimental Biology, vol. 224, no. 15, 242615 . https://doi.org/10.1242/jeb.242615 |
| ISSN: | 1477-9145 |
| DOI: | 10.1242/jeb.242615 |
| Popis: | Crocodilians are unique among vertebrates in that their hemoglobin (Hb) O2 binding is allosterically regulated by bicarbonate, which forms in red blood cells upon hydration of CO2. Although known for decades, this remarkable mode of allosteric control has not yet been experimentally verified with direct evidence of bicarbonate binding to crocodilian Hb, probably because of confounding CO2-mediated effects. Here, we provide the first quantitative analysis of the separate allosteric effects of CO2 and bicarbonate on purified Hb of the spectacled caiman (Caiman crocodilus). Using thin-layer gas diffusion chamber and Tucker chamber techniques, we demonstrate that both CO2 and bicarbonate bind to Hb with high affinity and strongly decrease O2 saturation of Hb. We propose that both effectors bind to an unidentified positively charged site containing a reactive amino group in the low-O2 affinity T conformation of Hb. These results provide the first experimental evidence that bicarbonate binds directly to crocodilian Hb and promotes O2 delivery independently of CO2. Using the gas diffusion chamber, we observed similar effects in Hbs of a phylogenetically diverse set of other caiman, alligator and crocodile species, suggesting that the unique mode of allosteric regulation by CO2 and bicarbonate evolved >80–100 million years ago in the common ancestor of crocodilians. Our results show a tight and unusual linkage between O2 and CO2 transport in the blood of crocodilians, where the build-up of erytrocytic CO2 and bicarbonate ions during breath-hold diving or digestion facilitates O2 delivery, while Hb desaturation facilitates CO2 transport as protein-bound CO2 and bicarbonate. |
| Databáze: | OpenAIRE |
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