Studies of algal hydrogenases

Abstract

Several species of algae are found, for the first time, to exhibit hydrogenase activity after dark adaptation. Seven of the species examined do not have hydrogenase activity after 48 hours of attempted adaptation. Hydrogenase activity in adapted cell-free extracts has been demonstrated in two Chlamydomonas species. The extract is obtained by sonication of a whole cell suspension followed by centrifugation at 160,000 x g for one hour. The time course of adaptation is similar to that obtained from adapted whole cells. In whole cells of Chlamydomonas moewusii, the pH optimum of the adaptation process is 7.5. The pH optimum of the enzyme from whole cells is 9.7 after adaptation. In another Chlamydomonas species, the pH optimum of the enzyme obtained for a cell-free adapted hydrogenase is 7.0. The optimum pH is 7.0 for the adaptation process. Cell-free extracts do not adapt below 2.5°. Unadapted extracts may be stored for at least four days at 0.5° - 2.5° under hydrogen and then adapted at 25°. Adaptation of cell-free extracts is not inhibited by light. Three hydrogenase isoenzymes from cell-free adapted Chlamydomonas sp. are obtained as bands by electrophoresis on polyacrilamide gel. They are identical to three of the five bands obtained from adapted whole cell extracts of this organism. One hydrogenase band is obtained from cell-free adapted extracts of Chlamydomonas moewusii. It is identical to one of the three isoenzyme bands obtained from adapted whole cell extracts of the same species. The hydrogenases of algae appear to have isoenzyme patterns and order of relative substrate specificity similar to those of bacterial enzymes. The adaptation process proceeds in the presence of carbon monoxide which inactivates the enzyme. This indicates that the appearance of hydrogenase activity may be controlled by the level of some metabolite(s) not immediately connected with the hydrogenase reaction. Inhibition of hydrogenase activity by carbon monoxide is reversed by removing the gas. Cell-free adapted preparations are more stable to air than either adapted whole cells or dried cell preparations from adapted whole cells. ATP may exhibit a regulatory effect on the adaptation process. Adaptation does not occur until the extract is devoid of ATP.