Enzymatic cleavage of dimethylsulfoniopropionate (DMSP) in cell-free extracts of the marine macroalga Enteromorpha clathrata (Roth) Grev. (Ulvales, Chlorophyta)

The enzymatic cleavage of dimethylsulfoniopropionate (DMSP) to dimethylsulfide (DMS) in the marine macroalga Enteromorpha clathrata (Roth) Grey. (Ulvales, Chlorophyta) showed a maximum activity of 3.1 μmol DMS min-1 (mg protein)-1 at 25°C and a pH optimum of 6.2 to 6.4. The activity was more sensitive to temperature than to pH changes. With ammonium sulfate precipitation, approximately 90% of the activity was found in the 0-35% fraction, indicating a fairly hydrophobic enzyme. Activity was increased by addition of detergents during extraction. These results suggest that the DMSP lyase enzyme is probably membrane-bound in vivo. The enzyme activity is relatively insensitive to chloride salt concentrations. Addition of nucleosides and nucleotides did not increase enzyme activity. After hyperosmotic shock for 72 h, enzyme activity increased 1.7-fold and intracellular DMSP concentration was enhanced from initially 80 mmol DMSP (kg freshweight)-1 to 107 mmol DMSP (kg freshweight)-1. The results suggest that DMSP cleavage within the cell by algal DMSP lyase may contribute to the production of oceanic and atmospheric DMS.