Investigation of some covalent and noncovalent complexes by matrix-assisted laser desorption/ionization time-of-flight and electrospray mass spectrometry.

Covalent and noncovalent complexes involving bovine superoxide dismutase, bovine alpha-lactalbumin and two variants, A and B, of bovine beta-lactoglobulin have been examined by delayed extraction matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and electrospray mass spectrometry. Covalent complexation with acrylamide was obtained through the interaction of these proteins with acrylamide monomers while treatment with peroxynitrite yielded complexes with NO2. Some of the complexation sites with acrylamide were reliably identified by performing tryptic digestion followed by MALDI-TOF measurements in the reflection mode. These data demonstrate that the presence of free cysteine in the investigated sequences is not a precondition for the observation of Cys-acrylamide complexes. Although the bulk of the present work is dedicated to the characterization of Cys-acrylamide adducts, the preliminary data on noncovalent complexes between two of those proteins and 8-anilinonaphthalene-1-sulfonic acid (ANS) were easily observed under electrospray conditions, while under MALDI-TOF conditions only the complex with beta-lactoglobulin B was clearly evident. The presented data demonstrate the advantage of the parallel use of both ionization techniques for this type of investigation.