A light activated oxygen consumption, and its effect on nitrogenase activity in the Cyanobacterium Anadaena cylindrica Lemm

The consumption of O₂ by isolated heterocysts is known to be enhanced by bright light. This enhancement is not removed by treatment with azide or heat (100 C). This thesis is an extended analysis of this activity. Light activated 0₂ consumption (LAOC) was observed in isolated heterocysts and various preparations of CO₂ fixing cells of A. cylindrica and in boiled preparations of higher plant material. The data indicate that the source of electrons for the LAOC process was a pool of a reduced carbon compound. Electrons were transported from this compound to P700 of photosystem I, possibly via some of the photo- synthetic electron carriers. Light energy boosted the electrons from P700 to ferredoxin reducing substance (FRS). Reduced FRS spontaneously oxidized in a two electron transfer to O₂ The resulting H₂0₂ was converted to water by catalase. In the heterocyst, LAOC appeared to play a role in protecting the nitrogenase enzyme complex against inactivation by O₂ The operation of the LAOC system increased the rate of N₂-fixation in A. cylindrica cultures. This increase was up to three-fold.