Alanine racemase

Alanine racemase is an enzyme that catalyzes the chemical reaction involving the amino acid alanine. This enzyme is found in many bacteria, fungi, and archaea, and plays a crucial role in the synthesis of D-alanine, an essential component of the peptidoglycan layer in bacterial cell walls.

Function

Alanine racemase catalyzes the conversion of L-alanine to D-alanine, and vice versa. This reaction is a key step in the biosynthesis of D-alanine, which is a critical component of the peptidoglycan layer in bacterial cell walls. The peptidoglycan layer provides structural integrity to the bacterial cell and protects it from osmotic lysis.

Structure

Alanine racemase is a dimeric enzyme, with each monomer composed of two domains. The larger domain, known as the PLP-binding domain, binds the pyridoxal phosphate (PLP) cofactor. The smaller domain, known as the control domain, regulates the activity of the enzyme.

Mechanism

The reaction catalyzed by alanine racemase involves the abstraction of a proton from the alpha carbon of L-alanine by a lysine residue in the active site of the enzyme. This results in the formation of a quinonoid intermediate, which is then reprotonated on the opposite face by a tyrosine residue to yield D-alanine.

Clinical significance

Because D-alanine is essential for bacterial cell wall synthesis and is not used by humans, alanine racemase is a target for antibacterial drug development. Inhibitors of this enzyme could potentially be used to treat bacterial infections.

See also

• Amino acid racemase
• Peptidoglycan
• Pyridoxal phosphate

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