Which of the following reactions occurs in step 2 of the urea cycle?

In step 2 of the urea cycle, the conversion of citrulline to argininosuccinate takes place. This reaction is catalyzed by the enzyme argininosuccinate synthetase. During this step, citrulline combines with aspartate, which donates an amino group to the intermediate, forming argininosuccinate. This reaction is crucial as it links the urea cycle to amino acid metabolism, specifically the incorporation of an amino group from aspartate into the urea cycle.

Understanding the urea cycle's sequence is important for grasping how nitrogen is managed in the body and how ammonia, a toxic byproduct of amino acid metabolism, is converted into urea for excretion. This step illustrates the cycle's function in detoxifying ammonia and is fundamental in regulating nitrogen balance in the organism.