{"doi":"10.1101/2021.03.22.436447","title":"New insights into the allosteric effects of CO <sub>2</sub> and bicarbonate on crocodilian hemoglobin","abstract":"Abstract Crocodilians are unique among vertebrates in that their hemoglobin (Hb) O 2 binding is allosterically regulated by bicarbonate, which forms in the red blood cell upon hydration of CO 2 . 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 CO 2 -mediated effects. Here we provide the first quantitative analysis of the separate allosteric effects of CO 2 and bicarbonate on Hb of the spectacled caiman ( Caiman crocodilus ). Using thin-layer gas diffusion chamber and Tucker chamber techniques, we demonstrate that both CO 2 and bicarbonate bind to Hb with high affinity and strongly decrease Hb-O 2 saturation, and propose that both effectors bind to an unidentified positively charged site containing a reactive amino group in the low-O 2 affinity T conformation of the Hb. These results provide the first experimental evidence that bicarbonate binds directly to crocodilian Hb and promotes O 2 delivery independently of CO 2 . Using the gas-diffusion chamber, we observed similar effects in the Hbs of a phylogenetically diverse set of other caiman, alligator, and crocodile species, suggesting that the unique mode of allosteric regulation by CO 2 and bicarbonate evolved &gt;80-100 million years ago in the common ancestor of crocodilians. Taken together, our results show a tight and unusual linkage between O 2 and CO 2 transport in the blood of crocodilians, where build-up of blood CO 2 and bicarbonate ions during breath-hold diving or digestion facilitates O 2 delivery, while Hb desaturation facilitates CO 2 transport as protein-bound CO 2 and bicarbonate.","journal":"bioRxiv (Cold Spring Harbor Laboratory)","year":2021,"id":220447,"datarank":0.10397207708399181,"base_score":0.6931471805599453,"endowment":0.6931471805599453,"self_citation_contribution":0.10397207708399181,"citation_network_contribution":0.0,"self_endowment_contribution":0.10397207708399181,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":1,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.952,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2021-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":777445,"name":"Hans Malte","orcid":"0000-0003-3460-1819","position":1,"is_corresponding":false},{"id":361319,"name":"Chandrasekhar Natarajan","orcid":"0000-0002-4841-0426","position":2,"is_corresponding":false},{"id":438304,"name":"Tobias Wang","orcid":"0000-0002-4350-3682","position":3,"is_corresponding":false},{"id":272499,"name":"Jay F. Storz","orcid":"0000-0001-5448-7924","position":4,"is_corresponding":false},{"id":438302,"name":"Angela Fago","orcid":"0000-0001-7315-2628","position":5,"is_corresponding":false},{"id":663845,"name":"Naim M. Bautista","orcid":"0000-0003-0634-0842","position":0,"is_corresponding":true}],"reference_count":36,"raw_metadata":{"citation_network_status":"fetched"},"created_at":"2026-07-18T23:53:46.965811Z","pmid":null,"pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}