Measurements of ATP levels of intact Azotobacter vinelandii under different conditions

Abstract

1. 1. The ATP level of intact cells of Azotobacter vinelandii grown on a nitrogen-free, minimal salts medium with mannitol as carbon source has been examined using the luciferin-luciferase method. Harvested, washed and starved cells had aerobic ATP levels similar to cells taken directly from the culture medium. 2. 2. The aerobic ATP level was always high and about the same with endogenous substrates or with added substrates giving a 10-fold variation of respiratory rates. On anaerobiosis, the ATP level fell to about 1/4 of the aerobic level. 3. 3. Under anaerobic conditions the rate of utilization of ATP was 0.4–0.6 and 1.6–2.3 nmoles/min per mg dry wt. at 12° with endogenous substrate and with added β-hydroxybutyrate or lactate, respectively. The rate of formation on addition of O 2 to anaerobic cells in the presence of β-hydroxybutyrate was 12 nmoles/min per mg dry wt. When the latter was compared with the rate of O 2 uptake with the same samples, P:O ratios of 2 were obtained (corrected for the rates of utilization). 4. 4. The aerobic ATP level was low in early log phase cells, then increased during growth to a maximum of 4.8–6.2 nmoles/mg dry wt. at the end of log phase growth. 5. 5. Aeration of anaerobic cells gave maximal ATP levels within about 30 sec at 12°, but linear O 2 uptake continued for several minutes, until exhaustion of the O 2 in the suspending medium. 6. 6. Oxidative phosphorylation in intact cells of Azotobacter vinelandii is an efficient process, but phosphorylation does not appear to be tightly coupled to O 2 uptake.