Question

Write the reactions by which aspartate donates its nitrogen for synthesis of arginine and urea. Where does the aspartate nitrogen bind to citrulline? Where do the carbons of aspartate go after the nitrogen is left on citrulline (what is the product) and where does that product fit into the rest of metabolism?

Answer 1

Where does the aspartate nitrogen bind to citrulline?

Aspartate reacts with citrulline to form arginino-succinate. Amino group of aspartate reacts with the carbon 1 of citrulline.

Where do the carbons of aspartate go after the nitrogen is left on citrulline (what is the product)?

In the next step, arginine-succinate is cleaved into arginine and fumarate. Fumarate is the aspartate without amino group (carbon skeleton of aspartate). The amino group of aspartate is donated to citrulline to become arginine.

Where does that product fit into the rest of metabolism?

This arginine is then cleaved into ornithine and urea. This urea contains the amino group donated by aspartate.

This whole process occurs in the urea cycle.