Place proteins A, B, and C in order of probable increasing elution volume in cation exchange chromatography during an increasing salt gradient run at pH 5. The figure shows a two-dimensional gel of a mixture of proteins A, B, and C. The vertical axis represents SDS-PAGE separation run from top to bottom. The horizontal axis represents isoelectric focusing with a pH gradient that runs from left to right (high pH to low pH). Proteins A, B, and C have isoelectric points of 8.2, 6.7, and 5.2, respectively. Complete parts (a) and (b), below. Place proteins A, B, and C in order of increasing elution volume on a size exclusion column. Assume they are monomers under the conditions of separation.