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The urea cycle (also known as the ornithine cycle) is a cycle of biochemical reactions that produces urea (NH 2) 2 CO from ammonia (NH 3). Animals that use this cycle, mainly amphibians and mammals, are called ureotelic. The urea cycle converts highly toxic ammonia to urea for excretion. [1] This cycle was the first metabolic cycle to be ...
Hyperammonemia. Due to accumulation of argininosuccinate, citrulline, and arginine in the liver when the urea cycle is deficient. Hyperammonemia, or high ammonia levels, is a metabolic disturbance characterised by an excess of ammonia in the blood. It is a dangerous condition that may lead to brain injury and death. It may be primary or secondary.
Urea is synthesized in the body of many organisms as part of the urea cycle, either from the oxidation of amino acids or from ammonia. In this cycle, amino groups donated by ammonia and L-aspartate are converted to urea, while L-ornithine, citrulline, L-argininosuccinate, and L-arginine act as intermediates.
Citrullinemia is an autosomal recessive urea cycle disorder that causes ammonia and other toxic substances to accumulate in the blood. [1] Two forms of citrullinemia have been described, both having different signs and symptoms, and are caused by mutations in different genes. Citrullinemia belongs to a class of genetic diseases called urea ...
The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems. The conversion of nitrogen can be carried out through both biological and physical processes. Important processes in the nitrogen cycle include fixation ...
Ammonia (NH 3) diffuses into the blood, circulating to the liver to be neutralized by the urea cycle. (N.b. urea is not the same as uric acid, though both are end products of the purine nucleotide cycle, from ammonia and nucleotides respectively.) When the skeletal muscles are at rest (ADP<ATP), ammonia (NH 3) combines with glutamate to produce ...
The liver converts ammonia to urea through a series of reactions known as the urea cycle. Liver dysfunction, such as that seen in cirrhosis, may lead to elevated amounts of ammonia in the blood (hyperammonemia). Likewise, defects in the enzymes responsible for the urea cycle, such as ornithine transcarbamylase, lead to hyperammonemia.
Ornithine translocase deficiency, also called hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome, [ 1] is a rare autosomal recessive [ 2] urea cycle disorder affecting the enzyme ornithine translocase, which causes ammonia to accumulate in the blood, a condition called hyperammonemia . Ammonia, which is formed when proteins are ...