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Articles

On the Mechanism and Stoichiometry of the Oxidation of Hydrazine by Illuminated Chloroplasts ¹

^a Biology Department, Brookhaven National Laboratory, Upton, New York 11973

Hydrazine can support a rapid oxygen uptake in illuminated chloroplasts. The oxygen uptake rate is inhibited by 3-(3,4-dichlorophenyl)-1, 1-dimethylurea but is only slightly increased by added methyl viologen, and little H₂O₂ is produced. The pH optimum for hydrazine-dependent oxygen uptake is much higher than that of the Hill reaction. Addition of Mn (II) increases the rate of oxygen uptake in the light and causes the reaction to continue in the dark, the dark rate being dependent on the duration of the preceding light period. Flash yield experiments show that at least six electrons are transferred from hydrazine per flash compared to one electron per flash when water is the electron donor.

We conclude that most of the oxygen uptake in the presence of hydrazine is due to a direct oxidation of the hydrazine by oxygen which is catalyzed by some factor, possibly Mn (III), produced by chloroplasts in the light. Other artificial electron donors are shown to support such artefactual oxygen uptake to varying extents.

¹ Research carried out at Brookhaven National Laboratory under the auspices of the United States Atomic Energy Commission.