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Amino acids are precursors of many specialized biomolecules

Explore how amino acids serve as precursors for the synthesis of important biomolecules such as heme, creatine, glutathione, neurotransmitters, polyamines, and nucleotides.

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Amino acids are precursors of many specialized biomolecules

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  1. Amino acids are precursors of many specialized biomolecules • The porphyrin ring of the heme groups in mammals are made from 8 Gly and 8 succinyl-CoA • Deficiency of enzymes leading to heme biosynthesis cause diseases called porphyrias. • (The degradation of heme yields bilirubin, a linear tetrapyrrole derivative, and the typical pigments found in bile, urine, and feces, a deficiency of which will cause jaundice

  2. Creatine, the “energy buffer” in skeletal muscle, is made from Gly, Arg, and Met. • Glutathione, the “redox buffer”, is derived from Glu, Cys, and Gly. • Many important neurotransmitters, e.g., g-aminobutyrate (GABA), serotonin • , dopamine, norepinephrine, epinephrine are derived from amino acids via simple pathways: all include a PLP-depedent decarboxylation reaction.

  3. Polyamines (e.g., spermidine and spermine), needed for DNA packaging, is made from Met and ornithine. • Nitric oxide (NO), a stable free radical signals for vasodilation in vertebrates, is made from the guanidino group of Arg and O2 in a reaction catalyzed by an monooxygenase, nitric oxide synthase (NOS). • NOS is a dimeric enzyme with each subunit containing an array of redox coenzymes: NADP, FMN, FAD, tetrahydrobiopterin, and Fe3+-heme.

  4. Porphyrins In mammals are made from Gly and succinyl-CoA (reactions 1 and 6 occur in the mitochondria, the rest in the cytosols) d-aminolevulinate synthase (main control target for heme biosynthesis) Heme Fe2+

  5. Creatine, the “energy buffer” in skeletal muscle, is derivded from Gly, Arg, and Met.

  6. Glutathione is made from Glu, Cys, and Gly GSH is probably important in maintaining proteins in their reduced forms. • GSH is an important cofactor for glutathione peroxidase, an enzyme containing an essential selenocysteine residue in the active site, to remove toxic peroxides in cells.

  7. Many neurotransmitters are derived from amino acids

  8. Spermidine and spermine are derived from Met and ornithine.

  9. Nitric oxide (NO) is made from Arg and O2 in a reaction catalyzed by nitric oxide synthase (NOS), a monooxygenase containing five coenzymes: NADP, FMN, FAD, tetrahydrobiopterin, and a Fe 3+-heme.

  10. 18. Nucleotides are synthesized via either the de novo pathways or the salvage pathways • In the de novo pathway simple precursors, including amino acids, PRPP, NH4+, CO2, and one-carbon units (carried on H4 folate) are used. • In the salvage pathway the free bases and nucleosides released from nucleic acid breakdown are used.

  11. The free bases (A, G, C, U, T) are not intermediates during the de novo synthesis: the purine ring is assembled on ribose phosphate to make AMP and GMP; the pyrimidine ring is first synthesized as orotate, which is then attached to ribose phosphate before being converted to UTP and CTP (dTMP is made from dUMP). • The deoxyribonucleotides (dNDPs) are synthesized by reduction of ribonucleotides (NDPs).

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