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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.
The excretion of urea is called ureotelism. Land animals, mainly amphibians and mammals, convert ammonia into urea, a process which occurs in the liver and kidney. These animals are called ureotelic. [3] Urea is a less toxic compound than ammonia; two nitrogen atoms are eliminated through it and less water is needed for its excretion.
L-Ornithine is one of the products of the action of the enzyme arginase on L-arginine, creating urea. Therefore, ornithine is a central part of the urea cycle, which allows for the disposal of excess nitrogen. Ornithine is recycled and, in a manner, is a catalyst. First, ammonia is converted into carbamoyl phosphate (H 2 NC(O)OPO 2−
[4]: 91–93 The net reaction is, therefore, thermodynamically favorable, for it results in a lower free energy for the final products. [ 10 ] : 578–579 A catabolic pathway is an exergonic system that produces chemical energy in the form of ATP, GTP, NADH, NADPH, FADH2, etc. from energy containing sources such as carbohydrates, fats, and ...
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 ...
Ornithine transcarbamylase deficiency also known as OTC deficiency is the most common urea cycle disorder in humans. Ornithine transcarbamylase, the defective enzyme in this disorder, is the final enzyme in the proximal portion of the urea cycle, responsible for converting carbamoyl phosphate and ornithine into citrulline.
For more information see urea cycle. Pages in category "Urea cycle" The following 21 pages are in this category, out of 21 total.
Arginase, which catalyses the conversion of arginine to urea and ornithine, is one of the five members of the urea cycle enzymes that convert ammonia to urea as the principal product of nitrogen excretion. [5] There are several arginase isozymes that differ in catalytic, molecular and immunological properties.
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