EFFECT OF TEMPERATURE ON 2 ENZYMES FROM A PSYCHROPHILIC CHLOROMONAS (CHLOROPHYTA)

A psychrophilic green alga belonging to the Chloromonas genus and here named ANTI was collected in Antarctica. The activities of two enzymes , nitrate reductase and argininosuccinate lyase, were measured at vari ous temperatures and compared to the corresponding enzyme activities i n the mesophilic species Chlamydomonas reinhardtii Dangeard. For both enzymes, the temperature for apparent optimal activity was about 20 de grees C lower in ANTI than in C, reinhardtii. The enzymes were also su bmitted to various heat treatments before measuring their activities. Both psychrophilic enzymes were more sensitive to heat than the corres ponding mesophilic enzymes. It is worth stressing, however, that in bo th species nitrate reductase was much more sensitive to heat than argi ninosuccinate lyase, which probably indicates that the peculiar struct ure of each protein primarily determines its dependence to temperature . Secondary adaptations to low temperatures should then occur to confe r the psychrophilic character.