Nitrogen donors degradation products

Citrulline, a non-protein amino acid, was identified independently by Mitsimori Wada in watermelon juice (Wada, 1930) and by Dankwart Ackermann as a product of the degradation of arginine (Ackermann, 1931). Soon afterwards, Hans Krebs and Kurt Henseleit (Krebs and Henseleit, 1932) proposed the first metabolic cycle ever described, in which citrulline was an intermediary in the synthesis of urea. A few years later, the role of aspartate as the donor of the second nitrogen for urea synthesis was established by Sarah Ratner (Ratner and Pappas, 1949). 

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