ere reduced by incubating with 10 mM of dithiothreitol at 56°C and alkylated by 27.5 mM of iodoacetamide at room temperature in dark. The four aliquots of proteins were then digested respectively using alpha lytic protease, chymotrypsin, a combination of trypsin and Glu-C, or a combination of Glu-C and AspN. Three 10-μg aliquots of ACE2 pro