Biocatalysis is the use of microbes or their enzymes to do chemistry. A popular organism that has been used in biocatalysis is the Brewer's yeast, which has been used by bakers and brewers for hundreds of years. Yeast is a single-celled organism that can live in a variety of environments because of its ability to utilize all kinds of molecules as food. This ability to “eat” all kinds of molecules is due to a diverse collection of enzymes that yeast can use to make or break chemical bonds. A family of enzymes in yeast called reductases are particularly important because they can produce chiral alcohols, which are important building blocks used in the synthesis of drugs such as Bestatin, ProzacTM, StraterraTM, and Taxol. We are trying to understand how these enzymes determine the specific chiral alcohol they are going to make.