Chapter 38, Objective 13: How is the urea cycle regulated?

This patient has a deficiency of argininosuccinate lyase and has very high concentrations of blood glutamine and ammonium ion. You could treat her with all of the following EXCEPT

When urea is synthesized in the liver, all of the following may be occurring EXCEPT

The urea cycle is a metabolic pathway used in mammals to incorporate excess nitrogen into urea and remove it from the body. However, it appears to play a far more wide-ranging role in the group of algae known as diatoms. Scientists from the Max Planck Institute of Molecular Plant Physiology in Potsdam are part of an international team of researchers that has succeeded in identifying the urea cycle in diatoms as a distribution and recycling centre for inorganic carbon and nitrogen. The urea cycle plays a key role in the fixation of the two elements and also makes an important contribution to the fact that diatoms can recover from short-term nutrient withdrawal and respond immediately to the availability of a greater supply of food by increasing their metabolic and growth rates. Genes that have reached the diatom genome through lateral gene transfer contribute to this capacity.


Energy and regulation of the urea cycle.

The control enzyme of the urea cycle is ___________ and it is regulated by ________________

The major clinical problem in treating patients with urea cycle deficiencies is to reduce the effects of excess ammonia on the nervous system, because high levels of ammonia are toxic to neurons, and cause irreversible neuronal damage.


UREA CYCLE Normally the adult human is in nitrogen balance

Argininosuccinase releases the aspartate carbon skeleton as fumarate, a TCA cycle intermediate, but not the aspartate nitrogen, to yield the amino acid arginine. Fumarate can be converted to oxaloacetate, another TCA cycle intermediate, which can be transaminated to another molecule of aspartate that can react with another molecule of citrulline and carry another nitrogen into the urea cycle.

The ornithine cycle and arginine synthesis

Generally, substrate availability regulates the rate of the urea cycle; the higher the rate of ammonia production, the higher the rate of urea formation. N-acetyl-glutamate is an allosteric activator of carbamoyl phosphate synthetase I, and its synthesis is stimulated by arginine. During conditions of increased protein metabolism following ingestion of a high protein diet, or during fasting, when muscle protein is degraded to supply carbon skeletons for glucose production (gluconeogenesis), the urea cycle operates at an increased rate to eliminate excess nitrogen as urea. As fasting progresses, ketone body synthesis increases, diminishing the need for muscle protein breakdown to supply amino acids as a source of carbon skeletons for gluconeogenesis. This, in turn, decreases the need for increased nitrogen excretion as urea, and the urea cycle slows.

26/09/2017 · The Urea Cycle – A Biochemical ..

Deficiencies of the urea cycle are a threat to health because of the accumulation of ammonia, which is a neurotoxin. Normally free ammonia is fixed into either α-keto glutatate by glutamate dehydrogenase or glutamine by glutamine synthetase. The glutamine can be used by a variety of tissues to donate its amide nitrogen for the synthesis of nitrogen-containing compounds. The resulting glutamate donates its amino group, by transamination, primarily to pyruvate to form alanine, which carries the nitrogen to the liver. In the liver the nitrogen is removed from its carriers and fixed to carbamoyl phosphate by carbamoyl phosphate synthetase I, the first enzyme of the urea cycle.

The steps of synthesis in the urea cycle (also: ..

The extent to which the elevation occurs depends on which enzyme of the urea cycle is deficient, and the key to treating a urea cycle deficiency is to identify the deficient enzyme.