Plant cell-walls complex, acidic oligosaccharides from

Several feruloyl esterases have been purified and characterized (Table 1). However, comparison of their properties is difficult as the range of natural and synthetic substrates used to characterize these enzymes is diverse and the enzyme assays are not unifomi. The substrates range in size and complexity from small, soluble esters such as feruloylated oligosaccharides isolated from plant cell walls and phenolic acid methyl esters or synthetic feruloylated arabinosides to larger, more complex and often less soluble substrates such as feruloylated polymeric plant cell wall fractions (28). The only criterion used in all cases is the release of free ferulic acid or another hydroxycinnamic acid by hydrolysis of an ester bond. Specificity, as defined by Ae rate of catalysis (kca divided by the Michaelis constant gives the best indication of preferred substrates. However, hydrolysis of polymeric substrates is more complicated since not all of the esterified substituents are chemically equal, and effects such as decreased solubility and steric hindrance further complicates any results obtained. Therefore, these data should not be extrapolated to obtain kinetic constants. 

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