Abstract
We have investigated the effect of Fe on the induction of ascorbate peroxidase (APX) in Fe-deficient Euglena cells that completely lacked APX activity. Addition of 0.13 mM Fe to Fe-deficient cells caused a two-phase induction of the APX activity: a sharp rapid increase in the first 3 h, followed by a steady gradual increase from 3 through 24 h. Cycloheximide had no effect on the initial increase of activity, but completely inhibited the subsequent increase. Immunoblot analyses using a monoclonal antibody (EAP1) raised against Euglena APX indicated that the former increase is due to activation of APX apo-protein and the latter one is due to de novo synthesis of the enzyme protein. However, Northern analysis revealed that the levels of APX transcripts remained constant, suggesting that the induction of Euglena APX by Fe is regulated at the post-transcriptional stage. The second increase of APX activity was also suppressed by the addition of succinyl acetone, an inhibitor of heme synthesis, suggesting that heme synthesis is essential for the synthesis of APX protein.
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