Thiol reagents, such as 1,4-dithiothreitol (DTT), are often added to the solutions of such proteins to protect them from this reaction and to reverse it when it occurs. (The reverse reaction works best at slightly alkaline pH.) Draw the product formed when DTT reacts with a protein disulfide bond to liberate the free thiol groups. Which of the following occurs in this reaction? (Check all that apply).1) The protein disulfide is oxidized2) The protein disulfide is reduced3) DTT is reduced4) DTT is oxidized