alpha-1,4-Glucan lyase cleaves alpha-1,4-linkages of nonreducing termini of alpha-1,4-glucans to produce
1,5-anhydrofructose (1,5-AnFru). The
enzymes isolated from fungi and algae show high homology with
glycoside hydrolase family 31. Purification of
alpha-1,4-glucan lyase from rat liver using
DEAE Cellulose chromatography resulted in separation of two enzymatic active fractions, one was bound to the column and the other was in the flow-through. Partial amino acid sequence determined from the
lyase, retained on the
anion exchange column, were identical with that of the N:-linked
oligosaccharide processing
enzyme glucosidase II. The
lyase showed similar enzymatic properties as the microsomal
glucosidase such as inhibition by
1-deoxynojirimycin and
castanospermine. On the other hand,
glucosidase II purified from rat liver microsomes produced not only
glucose but also a small amount of 1,5-AnFru using
maltose as substrate. Furthermore, CHO cells overexpressing pig liver
glucosidase II showed a 1.5- to 2-fold higher
lyase activity compared to the nontransfected CHO cells. Conversely, no
lyase activity was detectable either in PHAR2.7, the
glucosidase II-deficient mutant from a mouse
lymphoma cell line, or in Saccharomyces cerevisiae strain YG427 having the
glucosidase II gene disrupted. These data demonstrate that
glucosidase II possesses an additional enzymatic activity of releasing 1,5-AnFru from
maltose.