Pyridoxal compounds as specific reagents for the alpha and beta N-termini of hemoglobin.

Bifunctional pyridoxal derivatives with a charged side chain in the 5' position react specifically with the N-terminal valine residues of hemoglobin. Three of these compounds, which have only a single negative charge in the side chain, are highly selective for the alpha-chain N-terminal residues in the oxy conformation while pyridoxal phosphate, with two negative charges, reacts specifically with the beta N-terminal in deoxyhemoglobin. Schiff's base formation, therefore, results in decreased oxygen affinity with pyridoxal phosphate but increased oxygen affinity with the other three compounds. Reduction with sodium borohydride leads to irreversible coupling at either end of the molecule, and preparation and properties of such derivatives are described.