Pyruvate degradation via pyruvate formate-lyase (EC 2.3.1.54) and the enzymes of formate fermentation in the green alga Chlorogonium elongatum

Formate was formed in extracts of Chlorogonium elongatum via direct cleavage of pyruvate by a pyruvate formate-lyase (PFL, EC 2.3.1.54). The conversion of PFL to the catalytically active form required S-adenosylmethionine, ferric (2+), photoreduced deazariboflavin as reductant, pyruvate as allosteric effector and strict anaerobic conditions. At the optimum pH (pH 8.0), PFL catalyzed formate formation, pyruvate synthesis and the isotope exchange from ¹⁴C]formate into pyruvate with rates of 30.0, 1.5 and 1.2 nmol min^-1 mg^-1 protein, respectively. Treatment of the active enzyme with O₂ irreversibly inactivated PFL activity (half-time 2 min). In addition to PFL, the activities of phosphotransacetylase (EC 2.3.1.8), acetate kinase (EC 2.7.2.1), aldehyde dehydrogenase (CoA acetylating, EC 1.2.1.10) and alcohol dehydrogenase (EC 1.1.1.1) were also detected in extracts of C. elongatum. The occurrence of these enzymes indicates pyruvate degradation via a formate-fermentation pathway during anaerobiosis of algal cells in the dark.Abbreviations DTT dithiothreitol - Hepes 4-(2-hydroxyethyl)-1-piperazine+ethane sulfonic acid - PFL pyruvate formate-lyase