Abstract
In marine algae, the conversion of the multifunctional metabolite dimethylsulfoniopropionate (DMSP) to dimethylsulfide (DMS) occurs via DMSP-lyase enzymes. Apparent substrate kinetic properties of DMSP-lyases in algae have revealed high levels of variability. Some algal dinoflagellates, including symbiotic zooxanthellae (genus Symbiodinium) produce high intracellular levels of DMSP and DMSP-lyase capabilities vary among specific Symbiodinium strains. To examine the enzyme kinetic properties of DMSP-lyases in zooxanthellae, we used five cultured Symbiodinium microadriaticum (fruedenthal) strains (ccMP 421, 828, 829, 830, 1633) to optimize in vivo DMSP-lyase assay parameters. Optimal activity occurred at ?30 °c with higher enzyme activity at pH 8 compared to pH 7. Further studies were carried out to examine the enzyme kinetic parameters Vmax and Km in two zooxanthellae strains, ccMP 829 and 1633, that differ in their DMSP-lyase basal activity (high and low activity, respectively). Both zooxanthellae strains showed lower half saturation constants for DMSP (range of Km = 0.008-0.124 mM) compared to most other marine phytoplankton tested to date. Vmax values (?mol DMS Lcell volume-1 min-1) increased slightly or by 2.7-fold in strains 1633 and 829, respectively, in conjunction with decreasing growth rates in batch cultures and parallel increases in intracellular DMSP concentrations in strain 829.
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