This proposal compares the regulation of glutamate metabolism in hepatomas and liver. It is based upon the concepts that: (a) glutamate or glutamine are the main metabolic fuels of tumors; (b) there is a progression-linked, DPN, TPN-malic enzyme localized exclusively in tumor mitochondria which plays a key role in glutamate oxidation; (c) citrate is not maintained in tumor mitochondria but is an important regulator of normal mitochondria; d) the enzymes involved in mitochondrial glutamate metabolism can be organized into multi-enzyme clusters and interact specifically with the inner mitochondral membrane and its components; (e) differences between normal and tumor membranes could alter these enzyme-membrane interactions; (f) fumarate is an important modifier of this system; and (g) glutamate dehydrogenase is abundant but reversibly inhibited in the mitochondria of some tumors where it can play a structural role by organizing mitochondrial enzymes into multi-enzyme clusters and be activated to modify tumor malic enzyme and tumor metabolism. All of these factors a through g can play an important role in glutamate oxidation in tumors and give tumors unique metabolic characteristics which could possibly be utilized for future pharmacological intervention into tumor growth. Techniques used include: (a) a kinetic study of the system of pure enzymes correlated with assays of enzyme-enzyme interaction (light scattering, co-precipitation in polyethylene glycol); (b) measurement of binding of the enzymes to the membrane (differential centrifugation); and (c) a study of regulation of glutamate metabolism in intact tumor and normal mitochondria. We will also study regulatory aspects of tumor mitochondrial malic enzyme. An additional technique will be to convert noral mitachandrial membranes into model tumor membranes by enriching them with cholesterol and determining if this results in the uniques characteristics of tumor membranes.
