Pepsin storage - (Aug/20/2010 )
I have left 100x pepsin solution at 4 degrees for a couple of months. Now I realize it should have been in the -20 degree. Has the pepsin gone bad? also, is it ok to store pepsin at that concentration? It doesn't necessarily stay in solution, so I have to mix it pretty well every time I take some.
The general rule for things in the lab is: "If in doubt, throw it out." It is possible that it is still OK, but the only way you can tell this is to test it in a system where you know the expected results, and have some more around to compare your old stuff with.