Purification and characterization of hydrogenase from the marine green alga, Chlorococcum littorale

Hydrogenase from the marine green alga, Chlorococcum littorale, was purified 1485-fold, resulting in a specific activity for hydrogen evolution of 75.7 micromol/min/mg of protein at 25 degrees C, using reduced methyl viologen as an electron donor. The K(m) value for methyl viologen was 0.5 mM. The purity of the enzyme was judged by native PAGE. The molecular weight was estimated to be 55 kDa by SDS-PAGE, and 57 kDa by gel filtration. The optimum temperature and pH value for hydrogen evolution were 50 degrees C and 7.5, respectively. The partially purified hydrogenase catalyzed hydrogen evolution from ferredoxin that had been isolated from the same cells, but not from NADH or NADPH. The K(m) value for ferredoxin was 0.68 microM. The enzyme was extremely oxygen sensitive, losing over 95% of its activity upon exposure to air within minutes, even at 4 degrees C. Two peptide fragments were obtained from the hydrogenase protein digested enzymatically, and their amino acid sequences were determined. No significant homology was found to any other known sequences of hydrogenases.