The amino acid sequence of the IX-chain of the major haemoglobin of a newt, T. granulosa, has been determined. The chain is 142 residues long and has an extra methionine at its N-terminus when compared with human IX-chain. Most of the tryptic peptides were sequenced by a combination of the subtractive Edman method and by deduction from the compositions of overlapping fragments produced by various enzymic treatments. The sequence of two 'core' regions was obtained by automatic sequencing of large peptides produced by trypsin cleavage at arginine residues only after blockage of lysine residues by citraconylation; by cleavage between aspartic acid and proline residues with 70% formic acid, and by cyanogen bromide cleavage at methionine residues.
The primary organic phosphate modifiers of haemoglobin function are DPG (2,3-diphosphoglycerate) in the toad Bufo marinus and ATP in the lizard Trachydosaurus rugosus. Myo-IP6 (myoinositol hexaphosphate) and myo-IPs (myo-inositol pentaphosphate) are more effective than ATP or DPG in reducing the oxygen affinities of the haemoglobins of B. marinus, T. rugosus and man, while ATP and DPG are about equally effective. Competition experiments indicate that ATP, DPG and myo-IP6 bind to the same site or sites on the haemoglobins of each of the species. These findings, and those of others, are interpreted as evidence that the evolution of an organic phosphate binding site on the haemoglobin of an ancient vertebrate pre-adapted haemoglobin for interaction with a set of organic phosphates having certain structural features in common.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.