title: Biphasic kinetic behavior of nitrate reductase from heterocystous, nitrogen-fixing cyanobacteria.
abstract: 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 (K(m), 0.05-0.25 mm) and a lower catalytic activity and the second showing a lower affinity for nitrate (K(m), 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.
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-Consejo Superior de Investigaciones Científicas, Apartado 1113, E-41080 Sevilla, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Martin-Nieto
authors.forename: E
authors.initials: E
authors.lastname: Flores
authors.forename: A
authors.initials: A
authors.lastname: Herrero