1. Consider some isotopic labeling problems. Individual ¹⁵N-labeled amino acids are administered into a mouse. Researchers want to follow where the NMR-active Nitrogen appears in the different urea cycle steps occurring in the liver. Draw structures for the following products and indicate where the label would be located.

¹⁵N-labeled glutamate is administered. Where does the ¹⁵N-label appear on citrulline?

b) ¹⁵N-labeled aspartate is administered. Where does the ¹⁵N-label appear on urea?

c) ¹⁵N-labeled glutamine is administered. Where does the ¹⁵N-label appear on arginine?