You have a protein whose molecular mass is about 6.8 kD according to SDS-PAGE. However, SDS-PAGE of

Question:

You have a protein whose molecular mass is about 6.8 kD according to SDS-PAGE. However, SDS-PAGE of the protein in the presence of 2-mercaptoethanol reveals two bands of 2.3 kD and 4.5 kD. Are these polypeptides too large for direct sequencing by an automated sequencer using Edman degradation? What steps must you take to determine the complete sequence of this protein?