As part of a practical exam, an instructor gives you a purified protein sample and asks you to tentatively identify it using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The resulting gel is shown. The left lane shows standards of known molecular weight (Mr). The right lane shows the unidentified protein. Use the table to determine the identity of the purified protein. Note that the functional unit of lactate dehydrogenase is a tetramer of four identical subunits with a total molecular weight of approximately 140,000 Da. Protein Mr lactate dehydrogenase 140,000 phosphorylase b 97,000 ovalbumin 45,000 carbonic anhydrase 30,000 chicken egg white lysozyme 14,000 The unidentified protein band in the right lane of the gel migrates to a position between 45,000 Daltons and 22,000 Daltons. The purified protein in the right lane could be