will they reach the same distance on the gel ?
If equal quantity, will they band width ?
I am not clear about your question - what global protein are we talking about? Are you referring to a very common protein eg albumin, actin, cytoskeletal proteins ? What type of gel? SDS-PAGE? Native gel or denaturing?
Protein migration in polyacrylamide gels is based upon size, shape and charge. By heating in an SDS buffer with a reducing agent eg DTT or mercapto-ethanol, secondary structure effects due to di-sulphide bonds are eliminated and the molecule is essentially linear. By treating with SDS, all molecules are given a net negative charge which enables them to migrate towards the positive pole in a gel tank. If protein molecules were not treated with SDS then they would migrate according to their charge - some towards the positive, others to the negative (out of the gel), As secondary structure and charge are "eliminated", the protein then migrates according to its molecule weight/size. It is possible to have many proteins of the same mol wt ( ie equal migration) transferred together in a western blot. To resolve an "overlying" protein from one of the same mol wt, you may have to run a native gel, soak it in an SDS containing buffer, and then western blot it onto a nylon membrane. The "native" gel will resolve proteins on the basis of the overall protein charge, shape and size. Otherwise you may have to fractionate your protein extracts before gel analysis.
In the absence of details, assuming that the two proteins in question are monomers and we are talking about conventional Western Blots where the SDS-PAGE is used initially, yes the two bands could easily be on top of each other and the color of a generic protein binding/detecting dye will show you the additive effect.
However, in a Western Blot, one probes the membrane with a protein specific antibody to assess the quantity (at least in a semi-quantitative manner). As long as your antibodies for the two proteins do not cross-react, you can quantify them well enough by either using a duplicate set of gels and membranes or re-probing the same membrane after stripping the first antibody etc. [Be warned that multiple attempts of re-probing the same membrane with various antibodies yields progressively poorer signal as one loses some of the protein on the membrane through each cycle.]
And then there is always a 2-D gel... a little more work initially but far more informative because chances of two proteins having the same size and isoelectric point tend to be much lower than any of the two single parameters.
I'm very glad in your answers to my question ! I learned a lot .I found my question very childish .
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