KINETIC-PROPERTIES OF SULFATE UPTAKE IN 2 TYPES OF EUKARYOTIC GREEN MICROALGAE

Sulfate uptake in two different green algae, Chlamydomonas reinhardtii strain 21 gr and Monoraphidium braunii strain 202-7d was studied by m easuring the radioactivity accumulated inside the cells when incubated in the presence of S-35-labelled sulfate. In both cases, uptake is a light-dependent saturable process that showed maximal rate at 300 mu m ol/L sulfate for C, reinhardtii and 50 mu mol/L for M. braunii. Experi mental data were analysed both graphically and by computer fitting to different kinetic models. Whereas two Km values of around 1 and 50 mu mol/L could be observed in C, reinhardtii, M. braunii showed a typical Michaelis behaviour, with one Km value of around 5 mu mol/L. Studies performed with C, reinhardtii cells in the presence of different inhib itors strongly support multiphasic kinetics for sulfate uptake in this alga.