sentence: The HB2T buffer contained 60 mM β - glycerophosphate , 15 mM p-nitrophenylphosphate , 25 mM 4-morpholinepropanesulfonic acid ( pH 7.2 ) , 15 mM MgCl2 , 15 mM EGTA , 1 mM dithiothreitol , 0.1 mM sodium orthovanadate , 2 % Triton X-100 , 1 mM phenylmethylsulfonyl fluoride , and 20 mg / ml leupeptin and aprotinin .