ornithine cycle

u·re·a cy·cle

the sequence of chemical reactions, occurring primarily in the liver, that results in the production of urea; the key reaction is the hydrolysis of l-arginine by arginase to l-ornithine and urea; l-ornithine is then converted to l-citrulline by a carbamoylation reaction, then to l-argininosuccinate by an amination reaction involving l-aspartic acid; finally, a lyase-dependent step generates arginine and fumarate.

Synonym(s): Krebs-Henseleit cycle, Krebs ornithine cycle, Krebs urea cycle, ornithine cycle

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