Question

Which statement is not true regarding fumarate in urea cycle?

• A. Fumarate holds as a connecting link between Krebs cycle and urea cycle.
• B. Fumarate holds as a connecting link between Krebs cycle and gluconeogenesis.
• C. Fumarate acts as a reactant for the next step of the urea cycle.
• D. Fumarate is formed as a cleavage product of argininosuccinate along with arginine.

Answer 1

Answer: (C)

Fumarate acts as a reactant for the next step of the urea cycle.

Urea synthesis is a five step cyclic process, with five distinctive enzymes. In the fourth step of the urea cycle, the enzyme arginosuccinase cleaves arginosuccinate to arginine and fumarate. The fumarate is converted to oxaloacetate via fumarase and malate dehydrogenase and transaminated to aspartate. The arginine acts as a reactant for the next step of the urea cycle to yield urea and ornithine.

So, the correct answer is 'Fumarate acts as a reactant for the next step of the urea cycle'.