All of the following regarding urea cycle is true, except:: (A) On consumption  of high amount of proteins, excess urea is formed, (B) Synthesis of argininosuccinate consumes energy, (C) Rate limiting enzyme is ornithine transcarbamoylase, (D) One nitrogen of urea comes from aspartate
Answer is C. Carbamoyl phosphate synthase I, the rate-limiting enzyme of the urea cycle, is active only in the presence of N-acetylglutamate, an allosteric activator that enhances the affinity of the synthase for ATP.