Glutamate dehydrogenase isoenzymes in the bovine retina and human leukocyte.

In the present study, we investigated the enzymatical properties of the heat-labile and heat-stable glutamate dehydrogenases (GDHs) from the bovine retina and human leukocytes. Retinal GDHs were mitochondrial enzymes with an optimal pH of 7.5. Heat-labile (membrane-associated form) and heat-stable (soluble form) GDHs were found in the bovine retina as well as in the human leukocytes. At least 5 GDH isoenzymes were found in the retina and leukocytes by nondenaturing polyacrylamide gel electrophoresis. After heat treatment, the high-speed pellet obtained from centrifugation of the human leukocytes at 100,000 x g retained the 3 smaller isoenzymes but had lost the 2 larger isoenzymes. Both heat-labile and heat-stable GDH were found in the neuroretina, retinal pigment epithelium and optic nerve with high activities. Our results suggest that these tissues may be the main active sites of the GDH deficiency.