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Appl Environ Microbiol. 1984 March; 47(3): 449-454
Copyright © 1984, American Society for Microbiology. All Rights Reserved.

Physiological Studies of Oxygen Protection Mechanisms in the Heterocysts of Anabaena cylindrica

Marcia A. Murry{dagger},*, Alexander J. Horne and John R. Benemann{ddagger}

Sanitary Engineering Research Laboratory, University of California, Berkeley, California 94720

ABSTRACT

The mechanism of O2 protection of nitrogenase in the heterocysts of Anabaena cylindrica was studied in vivo. Resistance to O2 inhibition of nitrogenase activity correlated with the O2 tension of the medium in which heterocyst formation was induced. O2 resistance also correlated with the apparent Km for acetylene, indicating that O2 tension may influence the development of a gas diffusion barrier in the heterocysts. The role of respiratory activity in protecting nitrogenase from O2 that diffuses into the heterocyst was studied using inhibitors of carbon metabolism. Reductant limitation induced by 3-(3,4-dichlorophenyl)-1, 1-dimethylurea increased the O2 sensitivity of in vivo acetylene reduction. Azide, at concentrations (30 mM) sufficient to completely inhibit dark nitrogenase activity (a process dependent on oxidative phosphorylation for its ATP supply), severely inhibited short-term light-dependent acetylene reduction in the presence of O2 but not in its absence. After 3 h of aerobic incubation in the presence of 20 mM azide, 75% of cross-reactive component I (Fe-Mo protein) in nitrogenase was lost; less than 35% was lost under microaerophilic conditions. Sodium malonate and monofluoroacetate, inhibitors of Krebs cycle activity, had only small inhibitory effects on nitrogenase activity in the light and on cross-reactive material. The results suggest that oxygen protection is dependent on both an O2 diffusion barrier and active respiration by the heterocyst.

FOOTNOTES

* Corresponding author.

{dagger} Present address: Cabot Foundation, Harvard University, Petersham, MA 01366.

{ddagger} Present address: EnBio, Inc., Fairfield, CA 94533.

Appl Environ Microbiol. 1984 March; 47(3): 449-454
Copyright © 1984, American Society for Microbiology. All Rights Reserved.



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Copyright © 1984 by the American Society for Microbiology. All rights reserved.