HIGH-FIELD FOURIER-TRANSFORM ION-CYCLOTRON RESONANCE MASS-SPECTROMETRY FOR SIMULTANEOUS TRAPPING AND GAS-PHASE HYDROGEN DEUTERIUM EXCHANGE OF PEPTIDE IONS/

Gas-phase hydrogen/deuterium, exchange of D2O with [M + H](+) ions of angiotensin II, angiotensin I, [Sar(1)]-angiotensin II, bradykinin, de s-Arg(1)-bradykinin, des-Arg(9)-bradykinin, luteinizing hormone releas ing hormone (LH-RH), and substance P has been examined by Fourier tran sform ion cyclotron resonance mass spectrometry at 9.4 tesla. Because the FTICR dynamic range increases quadratically with magnetic field, p arent ions from a mixture of several peptides may be confined simultan eously for long periods at high pressure (e.g., 1 h at 1 x 10(-5) torr ) without quadrupolar axialization ( and its attendant ion heating), f or faster data acquisition and better controlled comparisons between d ifferent peptides. A high magnetic field also facilitates stored wavef orm inverse Fourier transform (SWIFT) isolation of monoisotopic [M + H ](+) parent ions, so that deuterium incorporation patterns may be dete rmined directly without the need for isotopic distribution deconvoluti on. Finally, a higher magnetic field provides for a greatly extending trapping period, for measurement of much slower rates. Angiotensin I, angiotensin II, and [Sar(1)]-angiotensin IT are found to undergo a rap id exchange. Angiotensin II and [Sar(1)]-angiotensin II exhibit multip le deuterium uptake distributions, corresponding to multiple gas-phase conformations. In contrast, substance P exchanges slowly and LH-RH di splays no observable exchange. Comparison of the relative H/D exchange rates for bradykinin and its des-Arg-derivative supports the hypothes is that bradykinin adopts a folded gas-phase conformation that unfolds upon removal of either terminal arginine residue. (C) 1998 American S ociety for Mass Spectrometry.