Role of Carbonyl Cyanide m-Chlorophenylhydrazone in Enhancing Photobiological Hydrogen Production by Marine Green Alga Platymonas subcordiformis

摘要

We demonstrated that a significant volume of H_2 gas could be photobiologically produced by a marine green alga Platymonas subcordiformis when an uncoupler of photophosphorylation,carbonyl cyanide m-chlorophenylhydrazone (CCCP),was added after 32 h of anaerobic dark incubation,whereas a negligible volume of H_2 gas was produced without CCCP.The role of CCCP in enhancing photobiological H_2 production was delineated.CCCP as an ADRY agent (agent accelerating the deactivation reactions of water-splitting enzyme system Y) rapidly inhibited the photosystem II (PSII) activity of P.subcordiformis cells,resulting in a markedly decline in the coupled oxygen evolution.The mitochondrial oxidative respiration was only slightly inactivated by CCCP,which depleted O_2 in the light.As a result,anaerobiosis during the stage of photobiological H_2 evolution was established,preventing severe O_2 inactivation of the reversible hydrogenase in P.subcordiformis.The uncoupling effect of CCCP accelerates electron transfer from water due to a disruption of the proton motive force and release of DELTA pH across the thylakoid membrane and thus enhances the accessibility of electron and H~+ to hydrogenase.The electrons for hydrogen photoevolution are mainly from the photolysis of water (90%).Upon the addition of CCCP,Chl a/b ratio increased,which implies a decrease in the light-harvesting PSII antennae or an increase in PSII/PSI ratio,possibly resulting in higher efficiency of utilization of light energy.The enhancement of H_2 evolution by the addition of CCCP is mostly due to the combination of the above three mechanisms.However,the disruption of the proton gradient across the thylakoid membrane may prevent a sustained photobiological H_2 evolution due to a shortfall of ATP generation essential for the maintenance and repair functions of the cells.