R. H. Burris

RESPIRATORY ENZYME SYSTEMS IN SYMBIOTIC NITROGEN FIXATION

Earlier studies on the respiratory systems in symbiotic nitrogen fixation (Wilson, 1938) indicated that the root nodule bacteria (Rhizobium spp.) reduce methylene blue anerobically in the presence of many organic compounds. With few exceptions, the efficiency of a given substrate as a hydrogen donator was approximately the same whether molecular oxygen or methylene blue was used as the hydrogen acceptor. Except for short reports by Konishi and Kawamura (1938) and by Kroulik and Gainey (1940) the dehydrogenase systems of the root nodule bacteria have not been extensively investigated. The present report deals with the behavior of the dehydrogenase systems of these bacteria under various physical and chemical conditions. METHODS

Incorporation of Isotopic Carbon into Compounds by Biosynthesis

With simple equipment it is possible to biosynthesize C14- or C13-labeled compounds by growing plants in closed systems. Several suitable containers for plants and devices for generating and adding carbon dioxide are described.

Occurrence and Significance of Oxalacetic Acid in Plant Tissues.

Summary Because a yellow color is produced on the addition of the nitrite reagent alone, the colorimetric method of Szent-Györgyi and Straub was found unsuitable for the determination of oxalacetic acid in plant tissue, unless relatively large quantities are present. The manometric method of Ostern proved satisfactory, and though as little as 10 micrograms of added oxalacetic acid per ml of plant sap could be detected by the method, the presence of oxalacetic acid in leguminous plants actively fixing nitrogen could not be demonstrated. It is suggested that the presence of oxalacetic acid in leguminous plants may be correlated with the phenomenon of nitrogen excretion.

Cell-Free Enzymes of Azotobacter vinelandii.∗

Summary Succinic, lactic and malic dehydrogenases and hydrogenase were demonstrated in cell-free juices of Asotobacter vinelandii by the use of the methylene blue reduction technic. Oxygen uptake with sodium succinate as substrate and hydrogen-oxygen uptake with hydrogen as substrate were observed in the Warburg respirometer. Cell-free juices contained oxalacetic acid and alpha-ketoglutaric acid decarboxylases, but not pyruvic acid decarboxylase. Though succinate oxidation was cyanide-sensitive, addition of heart muscle cytochrome c did not stimulate the oxidation of ascorbic acid, suggesting that the cytochrome system differs from the animal cytochrome system.