A protein sample shows bands at 150 kDa, 75 kDa, and 50 kDa on an SDS-PAGE gel. What can be inferred about the protein?

• A. The protein is a dimer with one subunit cleaved.
• B. The protein is a monomer with three different charges.
• C. The protein is composed of three subunits with different masses.
• D. The protein is a monomer with post-translational modifications.

Answer: (C)