Define Function of thiamin as Regulator of enzyme activity?

Thiamin regulates the enzymes involved in carbohydrate metabolism. These are:

a) Pyruvate dehydrogenase, which provides a key link between glycolytic pathway and citric acid cycle.

b) α-ketoglutarate dehydrogenase in citric acid cycle and transketolase  involved in pentose phosphate pathway.

c) Each enzyme contains a decarboxylase moiety that binds TPB at the active site, a lipoic acid binding moiety, a flavoprotein and one or more regulatory components that toggle the enzyme complex between the active form and the inactive form.

d) A fourth thiamin requiring enzyme is a branched-chain ketoacid dehydrogerzase, which plays a role in the metabolism of branched-chain amino acids.