THE AMMONIUM METHYLAMMONIUM UPTAKE SYSTEM OF SYMBIODINIUM-MICROADRIATICUM

Abstract

The substrate analogue [14C]-methylammonium was used to study ammonium/methylammonium uptake by Symbiodinium microadriaticum (zooxanthellae). The value of the Michaelis constant (Km) for the uptake system was approximately 35 μM with methylammonium as substrate; ammonium was a competitive inhibitor of methylammonium uptake, and the Km for ammonium uptake (determined as the inhibition constant, Ki, for methylammonium) was 6.6 μM. Methylammonium uptake by zooxanthellae was light-dependent. Methylammonium uptake rates of zooxanthellae which had been freshly isolated from the hermatypic coral Acropora formosa (0.85±0.05x10-10 μmol min-1 cell-1) were lower than those of axenic cultures of the zoo..