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  2. Urea cycle - Wikipedia

    en.wikipedia.org/wiki/Urea_cycle

    The urea cycle converts highly toxic ammonia to urea for excretion. [1] This cycle was the first metabolic cycle to be discovered by Hans Krebs and Kurt Henseleit in 1932, [2] [3] [4] five years before the discovery of the TCA cycle. The urea cycle was described in more detail later on by Ratner and Cohen.

  3. Purine metabolism - Wikipedia

    en.wikipedia.org/wiki/Purine_metabolism

    A key regulatory step is the production of 5-phospho-α-D-ribosyl 1-pyrophosphate by ribose-phosphate diphosphokinase, which is activated by inorganic phosphate and inactivated by purine ribonucleotides. It is not the committed step to purine synthesis because PRPP is also used in pyrimidine synthesis and salvage pathways.

  4. Argininosuccinate synthase - Wikipedia

    en.wikipedia.org/wiki/Argininosuccinate_synthase

    A few mutations lead to the production of an abnormally short enzyme that cannot effectively play its role in the urea cycle. Defects in ASS disrupt the third step of the urea cycle, preventing the liver from processing excess nitrogen into urea. As a result, nitrogen (in the form of ammonia) and other byproducts of the urea cycle (such as ...

  5. Argininosuccinate lyase - Wikipedia

    en.wikipedia.org/wiki/Argininosuccinate_lyase

    Mutations in the human ASL gene causes argininosuccinic aciduria, a rare autosomal recessive disorder, and results in deficiencies of the urea cycle. Argininosuccinate lyase is an intermediate enzyme in the urea synthesis pathway and its function is imperative to the continuation of the cycle.

  6. Purine nucleotide cycle - Wikipedia

    en.wikipedia.org/wiki/Purine_nucleotide_cycle

    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 glutamine , which is an energy-consuming step, and the glutamine enters the blood.

  7. Metabolic pathway - Wikipedia

    en.wikipedia.org/wiki/Metabolic_pathway

    The flux of the entire pathway is regulated by the rate-determining steps. [1]: 577–578 These are the slowest steps in a network of reactions. The rate-limiting step occurs near the beginning of the pathway and is regulated by feedback inhibition, which ultimately controls the overall rate of the pathway. [14]

  8. Ornithine decarboxylase - Wikipedia

    en.wikipedia.org/wiki/Ornithine_decarboxylase

    The enzyme ornithine decarboxylase (EC 4.1.1.17, ODC) catalyzes the decarboxylation of ornithine (a product of the urea cycle) to form putrescine. This reaction is the committed step in polyamine synthesis. [1] In humans, this protein has 461 amino acids and forms a homodimer. [2] In humans, ornithine decarboxylase (ODC) is expressed by the ...

  9. Carbamoyl phosphate synthetase I deficiency - Wikipedia

    en.wikipedia.org/wiki/Carbamoyl_phosphate_syn...

    The urea cycle is a sequence of reactions that occurs in liver cells. This cycle processes excess nitrogen, generated when protein is used by the body, to make a compound called urea that is excreted by the kidneys. In carbamoyl phosphate synthetase I deficiency, the enzyme that regulates the urea cycle is damaged or missing. The urea cycle ...