Hemicellulose is second to cellulose as the most common carbohydrate source on the planet.  Efficient utilization of this resource is essential to the economic viability of biomass refineries.  Xylan, a primary component of hemicellulose, is a polymer of β-1,4-linked xylose sugars.  This polymer is targeted by endoxylanase and β-xylosidase enzymes which will hydrolyze the substrate to simple sugar monomers for further downstream fermentation.  However, the enzyme accessibility to the xylan is blocked by various chemical substituents.  One of these chemical moieties is glucuronic acid which is found in the xylan of many plant tissues.  The presence of the glucuronic acid substituent not only impairs enzymatic hydrolysis, but also stabilizes the xylosidic bonds against acid hydrolysis.  The enzyme responsible for removing the glucuronic acid moiety is alpha-glucuronidase.  We have employed a high throughput enzyme activity assay to screen mixed culture DNA libraries for new alpha-glucuronidase genes.  We have cloned and biochemically characterized the corresponding enzymes.  We will describe the unique activity profiles of the enzymes and their ability to enhance xylan degradation.