Preparation and properties of pure, full-length IclR protein of Escherichia coli. Use of time-of-flight mass spectrometry to investigate the problems encountered.

IclR protein, the repressor of the aceBAK operon of Escherichia coli, has been examined by time-of-flight mass spectrometry, with ionization by matrix assisted laser desorption or by electrospray. The purified protein was found to have a smaller mass than that predicted from the base sequence of the cloned iclR gene. Additional measurements were made on mixtures of peptides derived from IclR by treatment with trypsin and cyanogen bromide.

Reflecting time-of-flight mass spectrometer with an electrospray ion source and orthogonal extraction.

An electrospray source has been coupled to a reflecting time-of-flight mass spectrometer. The ions enter as a continuous beam in a direction perpendicular to the spectrometer axis and are formed into short bursts of ions with velocities parallel to the axis by electrical pulses applied to injection electrodes. The instrument may be operated either in the linear mode, with ions detected behind the electrostatic mirror, or in the reflecting mode, with ions detected after reflection.

Kinetic energy measurements of molecular ions ejected into an electric field by matrix-assisted laser desorption.

Measurements of kinetic energy distributions of molecular ions ejected into an extraction field by matrix-assisted laser desorption are reported. The measurements were made in a time-of-flight mass spectrometer with an electrostatic mirror by measuring the reflected signal as a function of the difference between the accelerating voltage and the voltage applied to the mirror. The molecular ions were found to have less kinetic energy than the extraction field alone would normally provide, i.

Secondary-ion and electron production from surfaces bombarded by large polyatomic ions.

Heavy molecular ions with energies in the range 10-20 keV and masses from 276 u to 132,000 u, produced by matrix-assisted laser desorption, were used as primary projectiles to produce secondary-ion spectra from a variety of surfaces in a tandem time-of-flight mass spectrometer. In the negative mode the ratio of electron emission to secondary-ion emission was found to decrease rapidly with increasing projectile mass. Ion emission was found to dominate for primary ions larger than approximately 10,000 u.