Salvage pathways for nucleotides synthesis

[1] Salvage pathways for purine nucleotides synthesis (recycling)

Most cells have an active turnover of many of their nucleic acids (particularly some types of RNA) which, through degradative processes, result in the release of adenine, guanine and hypoxanthine. These free purines are reconverted to their corresponding nucleotides through salvage pathway. The de novo synthesis of purines requires a substantial investment of ATP. Purine salvage pathways provide a more economical means of generating purines.

Phenylketonuria (PKU)

Since, many amino acids are either neurotransmitters or precursors or antagonists of neurotransmitters, genetic defects of amino acid metabolism can cause defective neural development and mental retardation. Phenylalanine hydroxylase, the first enzyme in the catabolic pathway for phenylalanine, is responsible for the disease phenylketonuria (PKU), the most common cause of elevated levels of phenylalanine (hyperphenylalaninemia).