SUMMARY: Oxygen uptake by (NCIB 8003) grown in continuous culture without fixed nitrogen and with a low mannitol concentration (2°5 g./1.) and treated with lysozyme and EDTA was inhibited by ATP but not by ADP; ADP frequently prevented inhibition by ATP. In preparations obtained by disrupting bacteria suspended in a mixture of defatted bovine serum albumin, sucrose and MgCl in the French press, ATP inhibited oxygen uptake with either sodium succinate or sodium isocitrate as substrates and ADP prevented this inhibition; oxygen uptake with glucose-6-phosphate was inhibited by ATP or ADP. A form of respiratory control by nucleotides may thus occur in Azotobacter. Acetylene reduction (a measure of nitrogenase activity) by bacteria treated with lysozyme and EDTA was inhibited by ATP; this was attributed to inhibition of oxygen uptake by ATP causing inhibition of nitrogenase by oxygen. High oxygen solution rates inhibited nitrogenase in whole bacteria or in bacteria treated with lysozyme and EDTA; when the oxygen solution rate was lowered nitrogenase functioned immediately. These observations are probably expressions of processes which protect nitrogenase in whole bacteria from damage by oxygen.


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