L-Aspartate 4-decarboxylase catalyzes the conversion of aspartate to alanine and CO2. The wild-type enzyme was observed as dodecamers at pH 5.0. The mutation of Ser298 into Arg resulted in an almost complete loss of the enzyme activity, and caused regional structural distortion and defects in the enzyme assembly, as shown in circular dichroism spectra and gel filtration profiles. Mutating Tyr207 and Pro257 into His also resulted in inactivation of the enzyme. but did not affect the overall structure. Computer modeling Suggests that Ser298 is located on the surface, and its mutation may result in enzyme disassembly, whereas Tyr207 and Pro257 are near the active site, and their mutations may cause local structure perturbation. (C) 2008 Elsevier Inc. All rights reserved.