ASPARTATE-AMINOTRANSFERASE AND GLUTAMATE-DEHYDROGENASE ACTIVITIES IN THE SQUID GIANT NERVE

The present study sought to investigate the presence and distribution of some enzymatic activities involved in the metabolism of glutamate i n the giant nerve fiber of the tropical squid Sepioteuthis sepioidea. Specific activities of aspartate aminotransferase and glutamate dehydr ogenase were evaluated in homogenates of the isolated giant fiber, ext ruded axoplasm, and axoplasm-free giant nerve fiber sheaths. The activ ities of both enzymes were present in the tissue. The specific activit y of aspartate aminotransferase was similar in axoplasm and sheaths. H owever, the specific activity of glutamate dehydrogenase was an order of magnitude higher in the sheaths. This finding is discussed in the f ramework of the hypothesis that proposes that a differential distribut ion of the enzymes of the glutamatergic system between the axonal and neuroglial compartments forms part of a system of communication betwee n these cells whose neuronal signal may be glutamate.