Protein expression vs. protein activity? - (Aug/29/2007 )

I am learning to know that these two are not the same. Does that mean that eventhough I can detect a protein on a Western Blot, it doesn't mean necessarily that the protein is active? Or does it mean that I cannot even say that it is expressed, just that I can detect it? Help:P.

If you can detect your protein on a western blot, and it is migrating to the apparent molecular weight that you expect, you can say for definite that the protein is being expressed. This means that the primary structure (i.e. the amino acid chain) has been synthesised. Activity depends on, for example, correct folding of the enzyme, the presence of any required cofactors, proper targetting (e.g. if its a membrane protein) and that there are mutations crucial catalytic residues. Western blotting tells you nothing about these things.