Investigation of amide hydrogen back-exchange in Asp and His repeats measured by hydrogen (1H/2H) exchange mass spectrometry

▶ 100% back-exchange occurs in His repeats (His6) at HDX-MS quench conditions. ▶ Asp repeats (Asp6) retain deuterons for several minutes at HDX-MS quench conditions. ▶ Acetic acid accelerates the back-exchange rate at HDX-MS quench conditions. ▶ Residue-specific deuterium levels were obtained using a LTQ-Orbitrap with ETD.