CLONING AND BIOCHEMICAL-CHARACTERIZATION OF AN ANIONIC PEROXIDASE FROM ZEA-MAYS

We have isolated, cloned and characterized a cDNA from Zea mays L., de noted ZmAP1, coding for an anionic peroxidase. The open reading frame of ZmAP1 starting 72 residues from the 5' end of the cDNA predicts a 3 7778 dalton protein of 356 amino acid residues. The protein has high s imilarity to other peroxidases and contains two peroxidase motifs that carry two highly conserved histidines in the active center. We expres sed recombinant ZmAP1 protein in E. coli as a fusion with maltose-bind ing protein. The fusion protein was biochemically active after additio n of hemin to tile apoprotein. The maize peroxidase ZmAP1 has a pH opt imum at pH 4.0 and a K-m of 0.2 mM for the substrate 2,2'-azino-bis(3- ethyl-benzothiazolin-6-sulfonic acid) at this pH. In maize seedlings t he ZmAP1 gene is expressed predominantly in roots, the mesocotyl, the coleoptile and to a lower extent in the node, whereas no expression in the primary leaf was found. In situ hybridization shows that the expr ession of ZmAP1 in the young maize root is confined to the epidermis, hypodermis and the pericycle.