Cleavage of Methionyl Bonds in Taka-amylase A with Cyanogen Bromide

Abstract

Eight methionyl linkages in reduced-carboxymethylated Taka-amylase A [EC 3. 2. 1. 1] were cleaved by the action of cyanogen bromide. The optimum conditions for the cleavage reaction were searched for but no satisfactory conditions could be found. From the reaction mixture prepared under the best conditions among those examined, five fractions were obtained by gel filtration but none of them were homogeneous. Four fragments could be isolated in homogeneous state from the two crude fractions by ion exchange chromatography and their amino acid sequences could be elucidated. The number of residues involved in the four peptide fragments amounted to thirty nine which corresponded to slightly less than 10% of the total residues in the protein. One of the four fragments contained no homoserine residue, indicating that this was derived from the C-terminal part of the parent protein molecule. Other fragments seemed to have larger molecular size and were insolube in water. Although a few attempts were made, further fractionation of the insoluble fragments was unsuccessful.