The esterification of the three polysaccharides, starch, amylose and amylopectin was carried out
in pyridine–DMSO by succinic anhydride. The carboxylic groups in the succinylated polysaccharides
were measured by FT–IR spectroscopy. The succinic derivatives were tested as aamylase
(1,4-a-D-glucan glucano hydrolase, E.C. 3.2.1.1) substrates. A colorimetric assay of the
a-amylase activity indicated that this enzyme is active on succinic esters of starch and amylose
and that the activity shows a linear decrease with the number of succinic units introduced into the
polysaccharide. Since the colorimetric test was not suitable for the detection of the a-amylase
activity when succinylated amylopectin was the substrate, we set-up an assay based on the labeling
by a paramagnetic probe of the free carboxylic groups of succinylated polysaccharides. The
kinetics of the a-amylase reaction were monitored by ESR spectroscopy through the increase of
the mobility of the paramagnetic probe. The spin label used was the commercially available
4-amino-tempo. By this method we demonstrated that a-amylase is active on succinylated
amylopectin. The utility of the assay for monitoring a-amylase activity when other methods (i.e.
colorimetric tests) fail, is discussed. 1999 Elsevier Science B.V. All rights reserved.