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REVERSIBLE KINETIC MODEL FOR THE SHORT‐TERM REGULATION OF METHYLAMMONIUM UPTAKE IN TWO PHYTOPLANKTON SPECIES, DUNALIELLA TERTIOLECTA (CHLOROPHYCEAE) AND PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE) 1
Author(s) -
Roche Julie La,
Harrison W. Glen
Publication year - 1989
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1111/j.0022-3646.1989.00036.x
Subject(s) - phaeodactylum tricornutum , ammonium , biology , chlorophyceae , substrate (aquarium) , diatom , kinetics , kinetic energy , botany , algae , ecology , chlorophyta , chemistry , physics , organic chemistry , quantum mechanics
Methylammonium, an ammonium analog, was used to study the short‐term kinetics of ammonium uptake in a diatom, Phaeodactylum tricornutum Bohlin, and a green alga, Dunaliella tertiolecta Butcher. Time courses of methylammonium disappearance were measured over a wide range of initial substrate concentrations for the two species. It was shown that feedback inhibition, described mathematically by a reversible enzyme kinetic model, can be used to explain the data. For the two species, there was good agreement between the kinetic parameters obtained from the analysis of the uptake versus substrate curve and those from the fit of the reversible kinetic model to the time‐course data. All time courses of CH 3 NH 3 + disappearance could be described by constants V m and k s . Ammonium time‐course data show some similarities to its analog, methylammonium. Our study suggests that the apparent change in V m and k s with time measured after the addition of saturating ammonium concentrations reflects an uncoupling between transport and assimilation of the substrate rather than a real change in the kinetic parameters of the transport mechanism.