Aspartate (Asp), a non-essential amino acid with the structure NH2-CH(CH2-COOH)-COOH, plays a crucial role in various biosynthetic pathways in cells. Beyond its fundamental role as a proteinogenic amino acid, aspartate serves as a key precursor in nucleotide biosynthesis and other metabolic processes.

This article explores which biosynthetic processes involve aspartate as a precursor, focusing on protein synthesis, de novo purine and pyrimidine nucleotide synthesis, and glutathione synthesis.

Aspartate in Protein Synthesis (Process A)

• Aspartate is one of the 20 standard amino acids incorporated into proteins during protein synthesis.

• It is directly coded by mRNA and incorporated into polypeptide chains by ribosomes.

• This role is universal and fundamental to all living cells.

Aspartate in De Novo Synthesis of Inosine Monophosphate and Orotic Acid (Process B)

• Aspartate contributes nitrogen atoms during the de novo synthesis of purine nucleotides, specifically inosine monophosphate (IMP).

• In purine biosynthesis, the nitrogen at position N1 of the purine ring is donated by aspartate.

• Aspartate is also involved in the de novo synthesis of pyrimidine nucleotides, where it contributes both carbon and nitrogen to form orotic acid, the pyrimidine ring precursor.

• Thus, aspartate plays a critical role in the early steps of both purine and pyrimidine nucleotide biosynthesis.

Aspartate in Synthesis of Adenosine Monophosphate from Inosine Monophosphate (Process C)

• IMP serves as a branch-point intermediate for the synthesis of adenine and guanine nucleotides.

• The conversion of IMP to adenosine monophosphate (AMP) involves the incorporation of an amino group from aspartate.

• This reaction is catalyzed by adenylosuccinate synthetase and adenylosuccinate lyase, which use aspartate as the nitrogen donor.

• Therefore, aspartate is directly involved in AMP biosynthesis from IMP.

Aspartate in Glutathione Synthesis (Process D)

• Glutathione is a tripeptide composed of glutamate, cysteine, and glycine.

• Aspartate is not a precursor or direct participant in glutathione biosynthesis.

• The synthesis involves γ-glutamylcysteine synthetase and glutathione synthetase enzymes, which do not incorporate aspartate.

Summary of Aspartate’s Involvement

Correct Answer

Based on the above analysis, aspartate is involved as a precursor in processes A, B, and C but not in D.

Thus, the correct choice is:

(4) A, B and C

Conclusion

Aspartate is a versatile amino acid serving multiple biosynthetic roles beyond protein synthesis. It is essential in the formation of purine and pyrimidine nucleotides and specifically contributes to AMP synthesis from IMP. However, it is not involved in glutathione biosynthesis. Recognizing these roles highlights aspartate’s central place in cellular metabolism and nucleotide production.