The mature protein demonstrates a high degree of similarity
over a region corresponding to the C-terminal parts of
all known [Fe]-hydrogenases [9]. This region usually contains
highly conserved amino acids including cysteinyl
residues, which form the structural and functional basis of
the catalytic center (H-cluster) (Fig. 4). Also, other important
amino acid residues were conserved, which either
contribute to the hydrophobic niche that contains the Hcluster,
or play an important role in proton transport during
the catalytic activity of the enzyme [20]. This type of [Fe]-
hydrogenase could be identified in both major phylogenetic
branches of the Chlorophyceae (Chlorococcales and Volvocales),
which indicates that the hydA gene might be widely
distributed within that algal class. A systematic screening of