MRCP UK EXAMINATIONS

Detailed explanation-1: -Arginine undergoes hydrolysis to yield urea and ornithine in the presence of arginase. Ornithine is transported back to the mitochondria, which is used up in the second step of the cycle to form citrulline by combining with carbamoyl phosphate.

Detailed explanation-2: -An additional enzyme of the arginine metabolism, arginase (ARG), is critical for the cyclic nature of urea synthesis, catalyzing the formation of the ornithine and urea that is excreted in urine.

Detailed explanation-3: -Argininosuccinate is broken down into arginine and fumarate by argininosuccinate lyase (AL). Arginine is broken down into urea and ornithine by arginase. Ornithine translocase transports ornithine into the mitochondria.