Page 65 - Academic Press Encyclopedia of Physical Science and Technology 3rd BioChemistry

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Glycoconjugates and Carbohydrates 849

directly using mass spectrometric methods. In this case, atively low molecular weights and limited by solubility),
however, direct identification of a specific hexose may not weight average (sedimentation or light scattering), and
be possible since all will have the same molecular weight. viscosity average (a mixed function that is also a measure
Therefore, such studies are generally combined with com- of solution conformation—a measurement of mean end-
positional analysis (acid-catalyzed hydrolysis followed by to-end distance). Solution structures are often helical for
chromatographic separation) and prior knowledge of the repeating linear polysaccharides and heavily dependent
type of saccharide involved. on solvent (ionic strength) for polyelectrolytes.
Some structural data may also be obtained by the
use of specific lectins (Table 1). These are a class of
carbohydrate-binding proteins, generally of plant origin, SEE ALSO THE FOLLOWING ARTICLES
that show high specificity for one or another saccharide.
This may include linkage configuration and recognition BIOPOLYMERS • KINETICS (CHEMISTRY) • PHARMACEU-
of oligosaccharide. TICALS • ORGANIC CHEMISTRY,SYNTHESIS • POLYMERS,
Information desired for polymeric structures beyond STRUCTURE • PROTEIN STRUCTURE • PROTEIN SYNTHE-
that of components and linkages will generally in- SIS • STEREOCHEMISTRY • THERMODYNAMICS
clude molecular weight and solution conformation. Since
polysaccharides (including chains found in proteogly-
cans) are polydisperse, the normal definition of molec- BIBLIOGRAPHY
ular weight (as that of a single chemical entity) does not
apply. Ideally, one should determine the mole fraction of Advances in Carbohydrate Chemistry and Biochemistry—yearly review
each species present as a function of degree of polymer- volume published by Academic Press, New York.
Pigman,W.,andHorton,D.eds.,(1970).“TheCarbohydrates,Chemistry
ization. Currently, there are no methods for achieving this
and Biochemistry,” 4 volumes, Academic Press, New York.
goal.Rather,physicalmeasurementsaremadethatprovide Stick, Robert V. (2001). “Carbohydrates: the Sweet Molecules of Life,”
number average (osmotic pressure, suitable only for rel- Academic Press, New York.