Digestion patterns of two commercial endopolygalacturonases on polygalacturonate oligomers with a degree of polymerization of 7 to 21

Abstract

Many fruits and fruit juices are enzymatically treated to aid the process of liquefaction, juice extraction, viscosity reduction, and juice clarification. Polygalacturonases are a major component of enzyme mixtures used for these industrial applications as well as an enzymatic tool for elucidating pectin nano structure. Endopolygalacturonases (EPG) fragment the pectin homogalacturonan chain, cutting the molecule within a contiguous stretch of demethylated galacturonic acid (GalA) residues. To increase our understanding of this process, GalA oligomers with a degree of polymerization (DP) ranging from 7 to 21 were digested with two commercial endopolygalacturonase preparations (EPG M1 and EPG M2). Identity of the EPGs as EPG II from Aspergillus niger (EPG M1) and endo-PG I from A. aculeatus (EPG M2) was suggested from peptide mass fingerprinting with MALDI-TOF MS. Aliquots were collected at various time points during the digestion and the resulting fragmentation patterns were determined. Individual oligomer masses were estimated and converted to molar concentrations. The distribution of cleavage products produced by the EPGs differed. Smaller fragments, especially GalA monomer, were produced earlier with EPG M1. Rate constants for each of 87 possible reactions were estimated by a computer simulation model. When compared to optimized data for individual reactions, the experimental data for EPG M1 provided a good fi t, thus indicating the model was a good approximation of the fragmentation process.