M. Steinke et al., Partial characterisation of dimethylsulfoniopropionate (DMSP) lyase isozymes in 6 strains of Emiliania huxleyi, MAR ECOL-PR, 175, 1998, pp. 215-225
We characterised and compared dimethylsulfoniopropionate (DMSP) lyase isozy
mes in crude extracts of 6 axenic Emiliania huxleyi cultures (CCMP 370, 373
, 374, 379, 1516, and strain L). This enzyme cleaves DMSP to form dimethyl
sulfide (DMS), acrylate and a proton, but the function of this reaction in
algae is still poorly understood. Most of the cultures produced high concen
trations of intracellular DMSP, which was constant over the growth cycle an
d ranged from 157 to 242 mM, except for 1516 which had 50 mM DMSP cell(-1).
Extracts of all strains produced DMS from exogenous DMSP in vitro. DMSP ly
ases appeared constitutive, but enzyme activity and behaviour varied greatl
y among strains, and did not correlate with intracellular DMSP concentratio
n. Strains 373 and 379 showed high DMSP lyase activities (12.5 and 6.1 fmol
DMS cell(-1) min(-1), respectively), whereas DMS production was more than
100-fold lower in 370, 374, 1516 and L. This difference was intrinsic and t
he general pattern of high- and low-activity strains remained true over mor
e than a 1 yr cultivation period. The cleavage reaction was optimal at pH 6
in the strains with high lyase activity and pH 5 was optimal for 374, 1516
and L. Strain 370 showed increasing activity with increasing pH. Experimen
ts with additions of 0.125 to 2 M NaCl indicated halotolerant DMSP lyases i
n 373, 379 and 374. However, the halophilic DMSP lyases in 370 and L requir
ed 1 M NaCl addition for optimal DMSP cleavage, and 1516 showed optimal act
ivity at 2 M NaCl. These results suggest that there are several structurall
y different DMSP lyase isozymes within E. huxleyi. However, it cannot be ru
led out that varying concentrations of DMSP lyase per cell may have contrib
uted to the differences in enzyme activity per cell. Comparison with other
algal taxa indicates several families of DMSP lyases, hinting at possibly d
ifferent cellular locations and functions, and varying DMS production under
natural conditions.