Mass spectrometry as a tool for studying the action of human aspartic proteases on peptides and proteins.

Abstract

In the late eighties, two novel mass spectrometric methods with the sensitivity in the femtomole range were introduced, electrospray mass spectrometry (ESMS) and matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI TOF). These methods have been used for a variety of applications in protein chemistry (reviewed in [1] and [2]). In MALDI TOF the analyte is mixed with UV light-absorbing substance (matrix). The matrix and the compound to be analyzed are allowed to cocrys-tailize on the probe surface of the mass spectrometer. The sample is irradiated with UV light from a laser. The light is absorbed by the matrix causing the sample to be vaporized and ionized. The generated ions are accelerated in an electric field and are separated and detected by a time-of-flight detector. MALDI TOF was used for analysis of proteins up to 105 Da. ESMS is performed by evaporating droplets formed by the electrospraying of the protein solution followed by the transfer of the ions into the high vacuum. The evaporation generated highly charged ions are analyzed by the quadrupole mass spectrometer. We have applied the two techniques to the study of action of proteases on natural peptide and protein substrates. The present paper describes the advantages and limitations of the methods.