It's the primary sequence. It's that specific sequence of amino acids in that polypeptide that basically dictates the type of non covalent interactions that will exist on that polypeptide. And it's these non covalent interactions that basically drive the correct formation of our disulfide bonds. So if these non covalent interactions cannot exist in that polypeptide, then that polypeptide has no way of knowing what the proper disulfide bonds are that have to be foreign. And so what happened in this experiment was because we initially removed the beta macapto ethanol before actually removing our urea, we saw that in our denatured mixture we had the urea. So the non covalent bonds could not actually form and they could not actually drive the correct formation of those disulfide bonds.