Pyruvate Dehydrogenase, con’t.
Mechanism involves two covalent intermediates
with the enzyme:
Addition of pyruvate to TPP and loss of CO2 forms
hydroxyethyl TPP.
(This same intermediate is formed by pyruvate decarboxylase
in yeast alcoholic fermentation).
Transfer of hydroxyethyl group to lipoic acid to form
acetyl lipoic acid.
(This is an internal oxidation-reduction:  acetaldehyde is
oxidized, lipoic acid is reduced.)
See mechanisms page 646.