1. Which description is correct? (A) α-Keratin is rich in connective tissue. (B) A protein should be dissolved in a buffer with pH higher than its pl in order to bind to a cation exchange column. (C) If protein A runs faster than protein B in SDS-PAGE, protein A must have lower molecular mass than protein B. (D) Carboxypeptidase could be used to cleave the “X-C" peptide bond (X is any residue). (E) The non-amino acid part of a conjugated protein is called its prosthetic group.