English: The active site for pyruvate dehydrogenase (image created from PDB Code 1NI4) holds TPP through metal ligation to a magnesium ion (purple sphere) and through hydrogen bonding to amino acids. While over 20 amino acids can be found in the active site, amino acids Tyr 89, Arg 90, Gly 136, Val 138, Asp 167, Gly 168, Ala 169, Asn, 196, and His 263 actually participate in hydrogen bonding to hold TPP and pyruvate (not shown here) in the active site. The amino acids are show as wires, and the TPP is in ball and stick form. The active site also aids in the transfer of the acyl on the TPP to a lipoamide waiting on E2.