HMG‐CoA reductase is the committed and therefore the regulatory step in cholesterol biosynthesis. If HMG‐CoA is reduced to mevalonate, cholesterol is the only product that can result. The reduction is a two‐step reaction, which releases the Coenzyme A cofactor and converts the thiol‐bound carboxylic group of HMG‐CoA to a free alcohol. Two NADPH molecules supply the reducing equivalents because the thioester must first be reduced to the level of an aldehyde and then to an alcohol. ![]()
