The metabolic pathways from pyruvate to isobutanol and ethanol in Saccharomyces cerevisiae. The enzymes that catalyse the pathway from pyruvate to L-valine in the mitochondria are: acetolactate synthase (Ilv2+Ilv6), acetohydroxyacid reductoisomerase (Ilv5), dihydroxyacid dehydratase (Ilv3), and branched-chain amino-acid aminotransferase (Bat1). Ilv2 is the catalytic subunit of acetolactate synthase, and Ilv6 is the regulatory subunit. The enzymes that catalyse the pathway from L-valine to isobutanol in the cytosol are pyruvate decarboxylases (Pdc6, 5, 1) and alcohol dehydrogenases (ADHs). Pyruvate decarboxylases and alcohol dehydrogenases also catalyse the pathway from pyruvate to ethanol in S. cerevisiae. The broken line indicates the export of 2-ketoisovalerate from mitochondria to cytosol.