-C-H H-C-O-R
/ \ / \
/ \ / \
H-C-OH \ H-C-OH \
| O | O
HO-C-H / HO-C-H /
\ / \ /
\ / \ /
C-H C-H
| |
H-C-OH H-C-OH
| |
CH_{2}OH CH_{2}OH
[alpha]-Glucoside [beta]-Glucoside

The radical represented by the R may be either a common alkyl radical (as
CH_{3}, C_{2}H_{5}, etc.), another saccharide group (as in the case of the
disaccharides, trisaccharides, etc.), or some other complex organic group
(as in the case of the natural glucosides described in Chapter VI). But, in
every case, the glucoside is easily hydrolyzed by the enzyme _maltase_ (or
[alpha]-glucase) if the molecular arrangement is that represented by the
[alpha]-attachment, or by the enzyme _emulsin_ (or [beta]-glucase) if the
glucoside is of the [beta] type; but emulsin is absolutely without effect
upon [alpha]-glucosides, and maltase does not produce the slightest change
in [beta]-glucosides. These statements hold true regardless of the nature
of the group which is represented by the R in the formulas above. Hence,
the biochemical properties of the glucosides, so far as their hydrolysis
by the enzymes which are present in many biological agents is concerned,
depends wholly upon the molecular configuration of the glucose itself.
Furthermore, neither the mannosides, which differ from glucosides only in
the arrangement of the H and OH groups attached to one of the asymmetric
carbon atoms in the hexose, nor galactosides in which two such arrangements
are different (see configuration formulas on page 57), are attacked by
either maltase or emulsin. But other enzymes specifically attack other
disaccharides, or polysaccharides, or glucoside-like complexes. For
example, _lactase_ acts energetically upon ordinary lactose and all
other [beta]-galactosides; but not upon any glucoside, mannoside