An acetylesterase was purified from Aspergillus aculeatus on the basis of its ability to deacetylate homogalacturonan. A series of well-characterized substrates was prepared and used to investigate its specificity, including pectin with various degrees of methylation and acetylation, pectic domains with various structures, and oligomers. It was then compared to a rhamnogalacturonan acetylesterase previously isolated from the same fungus. Both enzymes were active towards various acetylated pectins, and were able to release acetyl groups from acetylated homogalacturonan, oligogalacturonates as well as rhamnogalacturonan at different extent. It was thus concluded that while the two enzymes differed in their efficiency, they are both pectin acetylesterases, able to act in the "smooth" as well as in the "hairy" regions of pectin. (c) 2008 Elsevier Ltd. All rights reserved.