Identification of phytochelatin-related peptides in maize seedlings exposed to cadmium and obtained enzymatically in vitro

An analytical strategy based on the sensitivity of electrospray tandem mass spectrometry following a simplified and reproducible sample preparation pr ocedure was evaluated for the determination of Cd-induced phytochelatins (P C) and related peptides in four maize varieties. In addition to the three k nown families of PC (PC, desGly-PC and iso-PC(Glu)) that were observed, nov el PC and desGly-PC homologues lacking the N-terminal ii-linked Glu were is olated from maize root extracts for the first time. Additionally the comple te sequence of iso-PC3(Glu) was determined by tandem mass spectrometry. Pep tides obtained in vivo and in vitro as the result of the reaction of glutat hione with the enzyme phytochelatin synthase were compared. Minor forms det ected from in vitro reactions include compounds with intramolecular or inte rmolecular disulfide bonds resulting from the oxidation of SH groups, phyto chelatin homologues lacking the N-terminal gamma -linked Glu, and new PC-re lated peptides with a Cys-Cys motif. Since peptides lacking a gamma Glu res idue could be generated as artifacts in electrospray mass spectrometry, the application of capillary electrophoresis with online electrospray mass spe ctrometry allowed the separation and detection of such peptides as endogeno us molecules present in planta and as products of in vitro reactions. (C) 2 001 Elsevier Science Ltd. All rights reserved.