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Limitations on the Analysis of Acetylene Reduction by Soybean at Low Levels of Acetylene

LAWRENCE C. DAVIS
Annals of Botany
Vol. 61, No. 2 (February 1988), pp. 179-183
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/42770275
Page Count: 5
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Limitations on the Analysis of Acetylene Reduction by Soybean at Low Levels of Acetylene
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Abstract

The analysis of acetylene reduction at low concentrations of acetylene involves a number of assumptions and both technical and kinetic complexities. The major difficulty in converting acetylene reduction rates to apparent N₂ reduction rates is determining the Km for acetylene in the presence of N₂. This substrate competition is dominant over diffusion limitation effects, but both introduce equivalent deviations in the observed Km. Because N₂ is a non-linear partial competitive inhibitor of acetylene reduction, correction for its presence is difficult. Two further complications are introduced by the non-linear response of nitrogenase to acetylene concentration even in the absence of N₂, and changes in the apparent Km of acetylene and Kt of N₂ as a function of other variables in the enzyme assay. It is proposed that transient analysis may be used for measurement of diffusion coefficients and calculations of possible diffusion limitations. It is demonstrated that one proposed model for estimating diffusion limitation (Denison et al., 1983, Plant Physiology 73, 648-51) confounds substrate competition with diffusion limitation.

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