Pyruvate and nitrogenase activity in cell-free extracts of the blue-green alga Anabaena cylindrica

When extracts of $\text{Anabaena cylindrica}$ are prepared in the absence of dithionite, they catalyze pyruvate-dependent acetylene reduction, a reaction not observable in assays containing dithionite. Ferredoxin and coenzyme-A, but not NADP and ferredoxin-NADP reductase, are required for maximal pyruvate-dependent activity. These acetylene-reducing extracts do not exhibit NADP-pyruvate dehydrogenase activity. However, pyruvate:ferredoxin oxidoreductase is present at levels of activity sufficient to support the $\text{in vitro}$ rate of pyruvate-supported acetylene reduction. These $\text{in vitro}$ data support earlier $\text{in vivo}$ evidence that pyruvate:ferredoxin oxidoreductase transfers electrons from pyruvate to nitrogenase in $\text{A. cylindrica}$.