Protein identification - (Nov/05/2008 )

A researcher is interested in studying a Cytochrome C protein from the bacterial organism E.coli. Working in a general laboratory she purifies the protein of interest, runs the sample out on a 1D-gel and places in a plastic container to stain overnight. In the morning she destains the gel and can see a single intense band that corresponds to the correct molecular weight of cytochrome C, as well as three weak bands with different molecular weights. She cuts out all four bands and submits them to a Proteomics Service for identification. When she receives the data, all four samples are identified as Bovine alpha-S1-casein, one of the major protein components of milk. Explain this anomaly.