Amino Acids that form Pyruvate

1. Alanine: This amino acid loses its amino group by transamination to form pyruvate (Fig. 1). [Note: Tryptophan catabolism produces alanine and, therefore, pyruvate.]

Figure 1 : Transamination of alanine to pyruvate. PLP = pyridoxal phosphate.

2. Serine: This amino acid can be converted to glycine as THF becomes

N⁵,N¹⁰-methylenetetrahydrofolate (N5,N10-MTHF), as shown in Figure 20.6A. Serine can also be converted to pyruvate (see Fig. 2B).

Figure 2: A. Interconversion of serine and glycine and oxidation of glycine. B. Dehydration of serine to pyruvate. PLP = pyridoxal phosphate; NH₃ = ammonia.

3. Glycine: This amino acid can be converted to serine by the reversible

addition of a methylene group from N5,N10-MTHF (see Fig. 2A) or oxidized to CO2 and ammonia by the glycine cleavage system. [Note:  Glycine can be deaminated to glyoxylate (by a d-amino acid oxidase;, which can be oxidized to oxalate or transaminated to glycine.

Deficiency of the transaminase in liver peroxisomes causes overproduction of oxalate, the formation of oxalate stones, and kidney damage (primary oxaluria type 1).]

4. Cysteine: This sulfur-containing amino acid undergoes desulfurization to yield pyruvate. [Note: The sulfate released can be used to synthesize 3′-phosphoadenosine-5′-phosphosulfate (PAPS), an activated sulfate donor to a variety of acceptors.] Cysteine can also be oxidized to its disulfide derivative, cystine.

5. Threonine: This amino acid is converted to pyruvate in most organisms but is a minor pathway (at best) in humans.