Abstract
Our way of diagnosing and treating inborn errors of the urea cycle enzymes is governed by how we conceive the functioning of the cycle. By the fact that the inherited enzyme deficiencies alter the normal conditions of the urea cycle, these inborn errors offer an opportunity to test our concepts of the regulation of the urea cycle. We have tried to simulate the urea cycle by computer models and test if the model is compatible with what we know from patients, assuming that concentration changes of metabolites in the liver would lead to alterations in the same direction in the body fluids, i.e., changes of amino acids in plasma or orotic acid as an indicator of carbamylphosphate [Bachmann, 1974,1980; Colombo, 1979] in the patients’ urine. Our aim was thus to test if our concept of how the urea cycle works is correct.