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Abstract

Dimethylsulfoniopropionate (DMSP) was detected in many strains of prototrophic bacteria and cyanobacteria. These data, together with results from earlier studies and the literature, clearly indicate that mainly photosynthetic micro- and macroorganisms have the metabolic capability to synthesize this compound. A relationship with temperature has also been identified. Polar macroalgae contain significantly higher DMSP contents compared to temperate or tropical species (5, 17). In this study, the cryoprotective function of DMSP was investigated on the activity of the model enzyme lactate dehydrogenase (LDH) as well as on that of malate dehydrogenase (MDH), extracted from the polar alga Acrosiphonia arcta (Chlorophyta). LDH activity was stabilized during freezing and thawing by the presence of DMSP concentrations up to 230 mM. The addition of higher amounts of DMSP to the enzyme assay even led to a 1.5 fold stimulation in the activity. DMSP stabilized MDH activity at the extremely low temperature of -2°C. In the presence of high solute concentrations, up to 300 mM, the enzyme activity rose to 165% of the control.