You have discovered a mutant protein that forms promiscuous disulfide bonds with many other cellular proteins in the endoplasmic reticulum. Using an antibody against the protein, you immunoprecipitate proteins that interact with it. You then separate these proteins using a special type of two-dimensional polyacrylamide-gel electrophoresis (PAGE): in this method, separation in the first dimension is carried out by SDS-PAGE in the absence of β-mercaptoethanol, while separation in the second dimension is carried out by SDS-PAGE in the presence of β-mercaptoethanol. The result is shown in the following schematic drawing. Apparent molecular weights are indicated on the left. What do you think is the molecular weight of the mutant protein? What is the molecular weight represented by the question mark?