Show your work Draw structures and the reactions by which ea

Show your work. Draw structures and the reactions by which each became labeled.

Labeled glutamate (see below) undergoes oxidative degradation in the liver of a rat. For the following metabolites, show the reactions that caused them to be labeled.

a) urea, b) succinate, c) arginine, d) citrulline, e) ornithine, f) aspartate

Solution

Part-a: The amino group of urea has associated with ¹⁵N, produce due to glutamate dehydrogenase producing ¹⁵NH4+; it can be produced due to transaminase action as a result ¹⁵N-labeled aspartate

¹⁵NH2 – CO – ¹⁵NH2

Part-b: After loss of the amino acid, the [2-¹⁴C] alpha-ketoglutarate is going to be metabolized in the Krebs‘s cycle. Succinate will be produced & it is labeled in the carboxyl groups

-OO¹⁴C - CH2 - CH2- ¹⁴COO-

Part-c: The arginine formed in the urea cycle contains ¹⁵N in both guanidino nitrogens

Part-d: Citrulline formed in the urea cycle contains ¹⁵N in the carboxamide group