Plant Physiol. Journal of Pharmacology and Experimental Therapeutics
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Plant Physiology 100:157-163 (1992)
© 1992 American Society of Plant Biologists

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Metabolism and Enzymology

Biphasic Kinetic Behavior of Nitrate Reductase from Heterocystous, Nitrogen-Fixing Cyanobacteria 1

José Martin-Nieto2, Enrique Flores and Antonia Herrero

Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-Consejo Superior de Investigaciones Científicas, Apartado 1113, E-41080 Sevilla, Spain, Facultad de Biología, Apartado 1113, E-41080 Sevilla, Spain

Nitrate reductase activity from filamentous, heterocyst-forming cyanobacteria showed a biphasic kinetic behavior with respect to nitrate as the variable substrate. Two kinetic components were detected, the first showing a higher affinity for nitrate (Km, 0.05-0.25 mM) and a lower catalytic activity and the second showing a lower affinity for nitrate (Km, 5-25 mM) and a higher (3- to 5-fold) catalytic activity. In contrast, among unicellular cyanobacteria, most representatives studied exhibited a monophasic, Michaelis-Menten kinetic pattern for nitrate reductase activity. Biphasic kinetics remained unchanged with the use of different assay conditions (i.e. cell disruption or permeabilization, two different electron donors) or throughout partial purification of the enzyme.

2 Present address: Division of Biology and Center for Basic Cancer Research, Kansas State University, 348 Ackert Hall, Manhattan, Kansas 66506.

1 Supported by grant No. BIO89-0527 from Comisión Interministerial de Ciencia y Tecnología, Spain.




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T.-H. Wang, H. Fu, and Y.-J. Shieh
Monomeric NarB Is a Dual-Affinity Nitrate Reductase, and Its Activity Is Regulated Differently from That of Nitrate Uptake in the Unicellular Diazotrophic Cyanobacterium Synechococcus sp. Strain RF-1
J. Bacteriol., October 1, 2003; 185(19): 5838 - 5846.
[Abstract] [Full Text] [PDF]


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Copyright © 1992 by the American Society of Plant Biologists