Chemistry Reference
In-Depth Information
Info Box 1
An old rule in chemistry and biochemistry says: 'Never waste pure thinking
time on impure preparations' . The following example reveals that - in contrast
to this rule - the use of a not yet pure preparation has led to an important dis-
covery. Experimentally, hemagglutination could well be exploited as an effi cient
means to remove erythrocytes from cell preparations. In 1959, Peter C. Nowell
from the University of Philadelphia Medical School planned to prepare a leu-
kocyte suspension from whole blood, devoid of residual erythrocytes. He used
a preparation from French beans (
Phaseolus vulgaris
) for removal of erythrocytes
by agglutination, at that time commercially available as a freeze-dried crude
extract. Expectedly, the cell fractionation worked. What had not been planned
was what happened with the leukocyte population: he noted that the number
of these cells had increased [P.C. Nowell. Phytohemagglutinin: an initiator of
mitosis in cultures of normal human leukocytes.
Cancer Res
1960;
20
, 462 - 466].
He hereby discovered the mitogenic activity of lectins. Apparently, the lectin
preparation acted both as an agglutinin for red blood cells and as a mitogen
for leukocytes. This observation led to further processing of the lectin-contain-
ing preparation. As described in 1975, lectin activity underlies the association
of two types of subunits, called E and L, to tetramers [R.L. Felsted
et al.
Purifi ca-
tion of the phytohemagglutinin family of proteins from red kidney beans
(
Phaseolus vulgaris
) by affi nity chromatography.
Biochim Biophys Acta
1975;
405
,
72 - 81]. If four E -subunits combine to form an E4 complex, a lectin results
which exclusively agglutinates red cells (E = erythroagglutinin); if four L - sub-
units are combined, the resulting L4 complex is inert towards erythrocytes but
active on leukocytes as mitogen (L = leukoagglutinin; please see also Table
18.1 ). The pure PHA -E isolectin, suited to remove the erythrocytes, would have
never enabled to discover mitogenicity in this setting.
In a similar way, the preferential agglutination of lymphoma cells by wheat
germ agglutinin (WGA) was discovered when a crude wheat germ lipase prepa-
ration that also contained WGA was employed as test material (please see
introduction of Chapter 25 for further details).
cases deviate from this scheme, that is those which are still referred to by special
designations [concanavalin A (ConA), jacalin, peanut agglutinin (PNA), phytohe-
magglutinin ( PHA ), and soybean agglutinin ( SBA )]. Table 18.1 also clarifi es the
issue as to whether information on monosaccharide binding covers a plant lectin's
carbohydrate specifi city entirely. By inspecting the presented sections on mono-
and oligosaccharides it becomes evident that plant lectins often have marked
preferences for oligosaccharides, with graded selectivity for related structures. For
example, complex - type
N
-glycans containing either a bisecting GlcNAc moiety or
the
1,6-branch can readily be detected by two different French bean isolectins
(for further information on this case, please see Info Box 1; for details on
N
- glycans
β
