title: Hydrogenosomes in the rumen fungus Neocallimastix patriciarum.
abstract: Sedimentable hydrogenase activity was demonstrated in cell-free extracts from both zoospores and vegetative growth of the anaerobic rumen fungus Neocallimastix patriciarum. Electron micrographs of the fraction enriched in hydrogenase activity contained finely granular microbody-like organelles, about 0.5 micron in diameter and having an equilibrium density of about 1.2 g X ml-1 in sucrose, 1.12 g X ml-1 in Percoll and 1.27-1.28 g X ml-1 in Metrizamide. These organelles, which are sedimentable at 10(5) g-min, bear no similarity to mitochondria, but are morphologically similar to hydrogen-evolving organelles possessed by certain anaerobic protozoa and termed 'hydrogenosomes'. Other typical hydrogenosomal enzymes, namely 'malic' enzyme, pyruvate:ferredoxin oxidoreductase and NADPH:ferredoxin oxidoreductase, were enriched in the same particle fraction as hydrogenase. The synthesis of pyruvate:ferredoxin oxidoreductase was found to be suppressed when the organism was cultured under an atmosphere of CO2, and an alternative pathway is proposed for growth under these conditions.
mesh_terms: D000818:Animals; D002499:Centrifugation, Density Gradient; D005287:Ferredoxin-NADP Reductase / Q000378:metabolism; D005658:Fungi / Q000201:enzymology / Q000378:metabolism* / Q000648:ultrastructure; D006864:Hydrogenase / Q000378:metabolism; D008291:Malate Dehydrogenase / Q000378:metabolism; D008854:Microscopy, Electron; D009940:Organoids / Q000201:enzymology / Q000378:metabolism* / Q000648:ultrastructure; D012417:Rumen / Q000382:microbiology
chemical_list: D008291:Malate Dehydrogenase; D006864:Hydrogenase; D005287:Ferredoxin-NADP Reductase