Salt bridges are hydrogen bonds between oppositely charged ions. One pair of salt bridges is formed by the carboxyl-terminal arginines of the alpha chains, another by the carboxyl-terminal histidines of the beta chains, and another by chloride ions at the amino-terminal valines of the alpha chains. Four pairs of salt links are also formed by DPG with cationic groups of the beta chains. The salt bridges stabilize the T structure. They lower its oxygen affinity and retard the T to R transition.
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