Subtilisin BPN'

The diisopropylphosphoryl derivative of subtilisin BPN' was digested with pepsin, and the resulting peptide fractions were separated by ion exchange chromatography on Dowex 50-X2. After additional purification a total of 58 pure peptides were isolated. Many of these peptides provided confirmation of the known structure which had been established from peptides obtained from the tryptic and chymotryptic digests. Additional peptides were isolated which provided sequences in the previously unknown regions of the protein, and several other peptides were obtained which gave crucial overlaps for the known tryptic and chymotryptic peptides. The known structure of subtilisin BPN' has given a clear picture of the sites of action of pepsin on this large protein.