Chain amino termini of the cat hemoglobins and the response to 2,3-diphosphoglycerate and adenosine triphosphate.

The amino acid compositions of the isolated cy and p chains from purified adult cat hemoglobins A and B have been determined. The data indicate that the Q! chains are similar but the /? chains differ by about four substitutions. Aminoterminal analysis has shown the presence of the typical Val-Leu sequence in the cat or chains. However, the two p chains differ at their amino terminals. NHz-terminal glycine is found in the A-b and a serine with a blocked (r-NH2 group occurs in this position in the B-P chain. The aminoterminal tryptic peptides of both p chains have been isolated and their sequences partially characterized. The effects of 2,3-diphosphoglycerate and ATP on the oxygen saturation curves of isolated cat hemoglobins A and B (HbA and HbB) have been investigated. Cat HbA, with free /I chain NH, termini, is sensitive to 2,3-diphosphoglycerate and ATP, whereas cat HbB, with blocked /3 chain NH2 termini, is insensitive to these effector molecules. The oxygen affinities of the hemolysates containing mixtures of HbA and HbB are changed by 2,3-diphosphoglycerate or ATP in proportion to the ratio of HbA to HbB in the hemolysate. The work provides support for a role of the NH2 terminus of the p chain in the control of oxygen binding in hemoglobin.