Final answer:
Glutamine phosphoribosyl amidotransferase is the enzyme that catalyzes the addition of the first component of the purine ring, and glutamine is the Nitrogen-containing amino acid that donates the first nitrogen of the ring during the de novo synthesis of purine nucleotides.
Step-by-step explanation:
The enzyme that catalyzes the addition of the first component of the purine ring is glutamine phosphoribosyl amidotransferase. The Nitrogen-containing amino acid that donates the first nitrogen as part of the ring is glutamine. In the de novo synthesis of purine nucleotides, glutamine provides the nitrogen atoms at N-3 and N-9 positions of the purine ring.
Here's a brief outline of the de novo pathway showing where glutamine's contributions fit: Activated D-ribose-5-phosphate is the starting material, and various donors contribute to the structure, which includes aspartate (N-1), glutamine (N-3, N-9), formate (C-2, C-8), and respiratory carbon dioxide (C-6) with glycine (C-4, C-5, and N-7). With each step, a specific enzyme mediates the addition, with glutamine phosphoribosyl amidotransferase being pivotal in introducing the first nitrogen.