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378 Electrophoresis

locate unique peptides affected by biological experiments studied by spectroscopic procedures. At lower frequen-
through direct superposition of many maps on top of one cies procedures have been devised to measure the rota-
another. As many as 2000 peptides have been resolved in tional diffusion of polar molecules; among these may be
one map from a single mixture, and individual variations mentioned dielectrophoresis, which unlike electrophore-
can be noted by suitable computer analyses of the digitized sis is concerned with the motion of both charged and un-
maps. charged particles in a nonuniform electric field. The di-
Two-dimensional maps of nucleic acid fragments are electric losses are measured as the frequency of the field
also made during sequencing procedure in order to read is increased, and when the frequency exceeds that where
gene codes. These maps are different in format from those the rotating dipolar molecules can follow the oscillating
prepared from protein mixtures because the radioactively field there is a marked change in the dielectric properties of
labeled and partially hydrolyzed nucleic acids are sepa- the solution. This frequency can be related to the distance
rated in one direction according to size, while the second between the poles in the dipole, provided that assump-
dimension contains parallel “ladders” formed from repli- tions are made about the shape of the molecule and values
cate experiments in which the nucleic acids are hydrolyzed for the local viscosity of the solvent can be obtained. In
by different enzymes. The result is a series of bands that general these observations have not been applied widely
can be correlated with other bands in order to produce because in solutions containing mixture of small and large
the correct sequence of nucleotides in the original nu- ions difficulties arise in interpreting the uncertain contri-
cleic acid. These gels are usually much longer than those butions from relaxations of gegenions or counterions with
used for protein separations, and the visualization is gen- respect to the macroion. In other words, the intention of
erally carried out after labeling with radioactive isotopes the experiments is frustrated by the lack of reliable inter-
or covalently linked fluorescent dyes. pretation. The work must be supplemented by data from
other sources in order to describe the electrical properties
F. Other Techniques of shielded dipoles.

In general the matrix methods utilize only two properties
of ions in their separation, namely, charge and/or size. It is SEE ALSO THE FOLLOWING ARTICLES
in the visualization of the separated products that the var-
ious methods differ. Some procedures employ immuno- CAPILLARY ZONE ELECTROPHORESIS • CHEMICAL THER-
logical reactions to visualize the products. Either this is MODYNAMICS • ELECTROCHEMISTRY • ELECTROLYTE
done after the separation by transferring the proteins to SOLUTIONS,TRANSPORT PROPERTIES • GAS CHRO-
other media prior to reacting with antibodies, or the anti- MATOGRAPHY • MICELLES
bodies are included in the acrylamide gel so the reactions
occur during the separation. Other methods rely on spe-
cific enzyme reactions that produce colored bands in order BIBLIOGRAPHY
to locate the enzymes; they cannot be performed on de-
natured products. Finally, fluorescent labeling before and Foret, F., Krivankov´a, L., and Boc, P. (1993). “Capillary Zone Elec-
after electrophoresis is superceding radioactive labeling trophoresis,” Wiley, New York.
for simple detection, which requires the development of Jandik, P., and Bonn, G. (1993). “Capillary Electrophoresis of Small
Molecules and Ions,” VCH Publishers, Weinheim/New York.
new physical detecters for scanning the gels.
Khaledi, M. G., ed. (1998). “High-Performance Capillary Electrophore-
sis: Theory, Techniques, and Applications,” Wiley, New York.
Lunn, G. (2000). “Capillary Electrophoresis Methods for Pharmaceutical
IV. ELECTROPHORESIS IN OSCILLATING Analysis,” Wiley, New York.
ELECTRIC FIELDS Rabilloud, T. (1999). “Proteome Research: Two-Dimensional Gel Elec-
trophoresis and Detection Methods,” Principles and Practice Series,
Electrophoresis is generally associated with transport in a Springer-Verlag, Berlin/New York.
stationary electric gradient, but the velocity of small ions Rothe,G.M.(1994).“ElectrophoresisofEnzymesLaboratoryMethods,”
Springer Laboratory Series, Springer-Verlag, Berlin/New York.
is sufficient for them to have been trasported during half
Tietz, D., ed. (1998). “Nucleic Acid Electrophoresis,” Springer Labora-
a cycle of an alternating field (see Section II.B). As the tory Series, Springer-Verlag, Berlin/New York.
frequency of the field is increased, this directional trans- Wehr, T., and Rodriguez-Diaz, R. (1998). “Capillary Electrophoresis of
port of the whole molecule in the solution is replaced Proteins,” Dekker, New York.
by rotation of the polarized molecule until eventually at Weinberger, R. (2000). “Practical Capillary Electrophoresis,” Academic
Press, San Diego.
frequencies above 1 GHz all the mass transport ceases.
Westermeier, R. (1997). “Electrophoresis in Practice: A Guide to Meth-
Above this frequency the motions of groups and individ- odsandApplicationsofDNAandProteinSeparations,”2nded.,Wiley,
ual atoms become increasingly important, and these are New York.