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Urea cycle regulation

I. Coupling of ornithine metabolism to mitochondrial oxidative phosphorylation

University of Colorado Health Sciences Center, Denver, CO.

Ornithine metabolism is coupled to oxidative phosphorylation in isolated rat liver mitochndria. The pathway involving ornithine:-ketoglutarate transaminase (OKT), glutamic semialdehyde dehydrogenase (GSDH), and glutamate dehydrogenase (GDH) with cycling of -ketoglutarate-glutamate at the OKT reaction appears to be involved. Ornithine may be utilized by this pathway to sustain ATP levels during mitochondrial energy-deficiency states with resultant decreased urea-cycle flux and increased ammonia production. This pathophysiologic mechanism suggests that hyperammonemia is a consequence of an energy-deficiency state. Therapy directed toward alleviating the energy-deficiency state may be more beneficial than efforts to reduce ammonia levels.

Address correspondence and reprint requests to Dr. Stumpf, Director of Pediatric Neurology, Box C229, University of Colorado Health Sciences Center, 4200 East Ninth Avenue, Denver, CO 80262.

Accepted for publication June 25, 1979

This work was supported by a clinical research grant from the Muscular Dystrophy Association, Grant No. HD04024 from the National Institute of Child Health and Human Development, NICHD Program Project Grant No. HD08315, and NIH Grant No. RR69 from the General Clinical Research Center's Program of the Division of Research Resources.