NITROGEN-METABOLISM IN ARENICOLA-MARINA CHARACTERIZATION OF A NAD DEPENDENT GLUTAMATE-DEHYDROGENASE

Muscle glutamate dehydrogenase (GDH) from the polychaete A. marina was studied with respect to its kinetic behavior and response to temperature and salinity. The multiphasic profiles of the saturation curves observed for NAD or glutamate can be interpreted as the result of a negative cooperativity process. No aminating activity was observed in the presence of either NADH or NADPH. ADP, which is recognized as a potent activator of GDH, exerts no activity on the system. An enhanced level of GDH activity was observed after several days of acclimation in a low salinity environment. A weak correlation between HN4+ excretion and GDH activity was found. These results suggest the existence in A. marina of a NAD-linked deaminating GDH with an excretory and osmoregulatory function.