Specificity of microbial alpha-amylase and amyloglucosidase hydrolysis of methyl amyloses

Methyl amyloses prepared under various conditions were exhaustively digeste d by means of cc-amylase (B. licheniformis) and amyloglucosidase (A. niger) . The amount of glucose that was released by the action of the enzymes was determined, Degradation products were further investigated as their O-methy l-O-deuteromethyl derivatives by mass spectrometry. The substituent distrib ution in the reduced and O-methylated-O-ethylated oligosaccharides was dete rmined, differentiating between non-reducing terminal glucosyl residues, 1 -->4-linked inner glucosyl units acid reducing glucose end groups. The port ion of glucose that could be liberated by the enzymes decreased with increa sing degree of substitution (DS) but at the same DS it was considerably hig her for heterogeneously prepared amylose ethers than for those prepared und er homogeneous conditions. Mass spectrometry (fast atom bombardment, FAB- a nd matrix-assisted laser desorption ionisation, MALDI-MS) gave evidence of different oligomer patterns and average values of degree of substituent/deg ree of polymerisation (DSDP) in dependence on the methylation conditions ap plied. More detailed analysis of the O-methylated positions of the oligosac charides showed that the reducing glucose end group was usually unsubstitut ed, while the non-reducing glucosyl residues could be 2-, 6- or even 2,6-di -O-substituted. In contrast, all 3-O-methyl groups were located in the inne r 1,4-linked glucosyl units, indicating inhibition of both enzymes. The res ults of this selective partial degradation are compared with those obtained after chemical random degradation and mass spectrometry.