Background: In plant cells, Catalases (CAT) are involved in the scavenging of the reactive oxygen species during development processes and in response to abiotic and biotic stresses. However, little is known about the regulation of the CAT activity by cations and calmodulins (CaMs). Methods and Results: Using bio-informatic analysis and in vitro catalase assays, we showed that durum wheat catalase 1 (TdCAT1) harbors highly conserved cation-binding domains which are localized at different

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... ns of the protein. Moreover, the protein exhibits a CAT activity in vitro that is specifically enhanced by Mn2+ and Fe2+ and to a lesser extent by Cu2+, Zn2+ and Mg2+ but not with Cd2+ cations. Moreover, we showed that TdCAT1 harbors a conserved calmodulin binding domain (CaMBD) and binds to CaMs in a Ca2+-independent manner via a GST-pull down assay. Moreover, TdCaM1.3/Ca2+ complex stimulated the catalytic activity of TdCAT1 in a CaM-dose dependent manner. Most interestingly, addition of Mn2+ cations enhance TdCAT1 activity in presence of CaM/Ca2+ complex. Conclusion: The catalase activity of TdCAT1 is enhanced in presence of various divalent cations. Besides, TdCaM1.3 proteins stimulates the catalase activity of TdCAT1 in Calcium dependent manner. Such effects were not reported so far and raise a possible role of CaM and cations in the regulation of plant CATs during cellular response to external signals.