THE NATURE OF THE HETEROGENEITY OF PETUNIA PEROXIDASE-A

Of the three molecular forms of petunia (Petunia hybrida) peroxidase a, the form PRXa 1.1 (37.5 kDa) was retarded on columns of concanavalin A-Sepharose, whereas forms PRXa 1.2 and 1.3 (37.0 and 36.5 kDa, respectively) were not. Chemical deglycosylation of the two fractions yielded only poorly resolved products of 33–35 kDa. Enzymatic deglycosylation with c-mannosidase converted PRXa 1.1 and 1.2 to immunoreactive products migrating in polyacrylamide gels at the position of PRXa 1.3. The presence of xylose, arabinose, fucose, mannose, glucose, and galactose was indicated by gas- chromatographic analysis. Lectin affinity blotting using lectins conjugated to horseradish peroxidase suggested that PRXa contains small complex-type N- glycosyl carbohydrate chains. These results indicate that the heterogeneity of PRXa is caused by differences in the terminal a-linked mannose residues. Some ce-mannosidase activity was present in the apoplast of leaves, which is consistent with the suggestion that it may be responsible for the conversion of PRXa 1.1 into PRXa 1.2 and 1.3 during leaf development. © 1990, Gustav Fischer Verlag, Stuttgart. All rights reserved.