Identification of two further cationic peroxidase isoenzymes secreted by peanut cells in suspension culture

Two cationic peroxidase isoenzymes have been identified, using ion-exchange and hydrophobic column chromatography, in the spent media of peanut cells maintained in suspension culture. One isoenzyme, designated CPz-I, has a molecular mass of 34 000 Da determined by SDS-PAGE and 33 610 ± 12 Da by MALDI-TOF mass spectrometry and a pI > 9.5 determined by isoelectric focusing. The N-terminal, and some internal amino acid sequences from trypsin-generated peptides have been obtained, but data-base sequence comparisons have identified no other peroxidases. The second isoenzyme, designated CPz-II, is a glycoprotein as determined by recognition by a monoclonal antibody (mAb 2.23) which is specific for the xylose/fucose containing complex plant N-glycan structure, and has a molecular mass of 33 500 Da determined by SDS-PAGE and 33 164 ± 17 Da determined by MALDI-TOF mass spectrometry, and a basic pI of 9.0 as determined by isoelectric focusing. N-terminal, and some internal amino acid sequences from trypsin-generated peptides, have been obtained and data-base searching revealed highest, but not complete, identity with the translated sequence of prxPNC-2, a cDNA isolated previously from the same peanut cell suspension culture system. This partial identity is confirmed by recognition of CPz-II by an antibody raised against the protein product of prxPNC-2 obtained by the expression of the cDNA in Escherichia coli.