Characterization of the Alternative Oxidase from the Psychrophilic Green Alga Chlamydomonas sp. UWO241

The alternative oxidase (AOX) was studied in the psychrophilic green alga Chlamydomonas sp. UWO241. AOX is the sole component of the alternative pathway of mitochondrial electron transport and is present in all plant and algal species. In silico analysis of the deduced protein sequence of the cloned AOX cDNA showed that the UWO241 protein has lower amounts of proline and higher amounts of lysine and tryptophan compared to the AOX sequence of the mesophilic alga C. reinhardtii. These changes have been seen in other studies of cold-adapted enzymes. Interestingly, unlike C. reinhardtii, AOX transcript abundance in UWO241 did not increase in response to a shift from ammonium to nitrate growth media or to treatment with hydrogen peroxide. A polyclonal antibody that recognizes AOX in C. reinhardtii did not cross-react with AOX from UWO241. This finding is consistent with the UWO241 protein being structurally distinct, highlighting its adaptation to low temperature