Reaction catalyzed by 3-methyl-2-oxobutanoate dehydrogenase (2-methylpropanoyl-transferring) (1.2.4.4)

	E1b-thiamine diphosphate	+			=		E1b-thiamine diphosphate-acyl	+
	E1b-thiamine diphosphate	+		2-oxo-acid	=		E1b-thiamine diphosphate-acyl	+		CO2