Effect of thermal acclimation on subunit cooperativity in Palaemon serratus glutamate dehydrogenase

Glutamate dehydrogenase (GDH) from the abdominal muscle of the shrimp Palaemon serratus displays a complex cooperatively pattern with respect to the cofactor (NAD) and substrate (glutamate) concentrations: at low concentrations negative cooperativitiy is predominant whereas positive cooperativity prevails at high concentrations. GDH is sensitive to thermal variations of the environment and to conditions of thermal acclimation. The maximum cooperativity indexes (positive and negative) are obtained at 13° for NAD irrespective of the acclimation temperature (13 or 18°). In contrast, for glutamate, positive cooperativity is only observed at temperatures near the acclimation temperature. At 13° for animals adapted at 18° and at 27° for animals adapted at 13° a complete loss of subunit cooperativity and a Michaelian kinetic pattern are observed.