Because of the synergistic presence of enzyme systems, whole-cell biocatalysts are an advantageous means of oxidizing alpha-hydroxy to alpha-keto carboxylic acids. The effect of different parameters on conversion were determined when whole cells converted L-lactate to pyruvate. The biocatalyst was a double recombinant Pichia pastoris containing a glycolate oxidase and catalase enzyme system. A marked increase in conversion occurred with oxygen compared to air. This indicated that the oxygen concentration was an important factor in the rate-limiting step. Lactate concentrations above 0.5 M showed substrate inhibition. Although temperature played an important role in enzyme stability, whole-cell tranformants were much more stable over time than soluble enzymes. (c) 2004 Elsevier Ltd. All rights reserved.