The synthesis of Oxaldie-3. a synthetic 31-residue peptide with oxaloacetate decarboxylase activity, is described. Biophysical characterisation by gel filtration, CD and NMR spectroscopy indicated that the peptide adopted a folded structure in solution. Oxaldie-3 was an efficient catalyst at concentrations as low as 2 muM, 100-fold lower than the previously described Oxaldie-2, which relied on aggregating alpha -helices for activity. Oxaldie-3 speeded decarboxylation by more than three orders of magnitude relative to simple amines. (C) 2001 Elsevier Science Ltd. All rights reserved.