Characterization of catalase from green algae Chlamydomonas reinhardtii

Some of the biochemical properties of catalase (H2O2:H2O2 oxidoreductase, EC 1.11.1.6) were determined in Chlamydomonas reinhardtii. The level of catalase activity was higher in cells grown in the dark than in the light. Three isoforms of the enzyme were detected in IEF regardless of culture conditions: two main isoforms with pI of 5.5 and 5.4 and a minor isoform with pI of 5.3. The isoform with pI of 5.5 predominated during the logarithmic phase of growth and was present throughout the culture period, while the second isoform with a pI of 5.4 appeared at the stationary phase. Subcellular fractionation on a sucrose density gradient revealed that catalase is localized in mitochondria. Mitochondria purified on a Percoll gradient contained three isoforms. The extracts from stationary phase cells were gel filtrated and catalase activity eluted as a single sharp peak with a molecular mass of 120kDa containing the three isoforms. After SDS-PAGE and Western blotting, antibodies against pumpkin catalase reacted mainly with a band corresponding to 57kDa, but a slight band with molecular mass of 59kDa also appeared. In purified mitochondria, the antibodies reacted with a single band corresponding to 57kDa. These results indicate that mitochondrial catalase in C. reinhardtii consists of two subunits with 57kDa. The catalase of C. reinhardtii is unique among enzymes from green plants in that it is a dimer located in the mitochondria instead of a tetramer located in microbodies.