DETERMINATION OF THE BLOCKED N-TERMINAL OF SOYBEAN LEGHEMOGLOBIN-B

Soybean leghemoglobins ā and b̄were compared by microscale peptide mapping after heme removal with acid-acetone. Maps generated by trypsin or the combined action of trypsin and thermolysin indicated a large amount of homology between the proteins with the only variations detected being the N-terminal peptides. The N-terminal tryptic peptide of leghemoglobin b̄ was found to be both blocked and to lack the first amino acid of the corresponding leghemoglobin ā peptide. Nuclear magnetic resonance and gas chromatography/mass spectroscopy studies showed that the N-terminal of leghemoglobin b̄ was N-acetyl-alanine. It is possible that leghemoglobin b̄ arises from leghemoglobin ā by a two-stage modification involving cleavage of the N-terminal valyl residue and subsequent acetylation of the exposed alanyl residue. © 1979.