2. • PSZO 204 : TOOLS AND TECHNIQUES IN BIOLOGY-II
• UNIT II : PRINCIPLES AND APPLICATION OF CHROMATOGRAPHY-II
• 2.2 AFFINITY CHROMATOGRAPHY:CHROMATOGRAPHIC
MEDIA,IMMOBILIZED LIGANDS,ATTACHMENT OF LIGANDS TO THE
MATRIX,EXPERIMENTAL PROCEDURES AND APPLICATION.
3. CONTENT
•
• Introduction
•
• Principle
•
• Chromatography media
•
• Immobilized ligands
•
• Attachment of ligands to the matrix
•
• Experimental procedures
•
• Application
•
4. INTRODUCTION
• Affinity Chromatography is essentially a sample purification technique, used
primarily for biological molecules such as proteins.
• It is a method of separating a mixture of proteins or nucleic acids (molecules) by
specific interactions of those molecules with a component known as a ligand,
which is immobilized on a support. If a solution of, say, a mixture of proteins is
passed over (through) the column, one of the proteins binds to the ligand on the
basis of specificity and high affinity (they fit together like a lock and key).
• The other proteins in the solution wash through the column because they were
not able to bind to the ligand.
5. PRINCIPLE
• Affinity chromatography is one of the most diverse and powerful chromatographic
methods for purification of a specific molecule or a group of molecules from
complex mixtures
• It is based on highly specific biological interactions between two molecules such as
interactions between enzyme and substrate,receptor and ligand,or antibody and
antigen.
• These interactions which are typically revesible are used for purification by placing
one of the interacting molecules referred to as affinity ligand onto a solid matrix to
create a stationary phase while a target molecule is in the mobile phase.
• Many of the commonly used ligands coupled to affinity matrices are now
commercially available and are ready to use.
6. CHROMATOGRAPHIC MEDIA
• A matrix in its use here is a substance,usually in bead form to which a
specific ligand is covalently bound.
• In order to for the matrix to be effective it must have certain characters:
• 1)It must be insoluble in solvents and buffers employed in the process
• 2)It must be chemically and mechanically stable..
• 3)It must be easily coupled to a ligand or spacer arm onto which the ligand
can be attached.
• 4)It must exhibit good flow properties and have a relatively large surface
area for attachment
7. IMMOBILIZED LIGAND
• The ligand can be selected only after the nature of the macromolecule to
be isolated is known.
• When a hormone receptor protein is to be purified by affinity
chromatography, the hormone itself is an ideal candidate for the ligand.
• For antibody isolation ,an antigen or hapten may be used as ligand.
• If an enzyme is to be purified,a substrate analog,inhibitor,cofactor,or
effector may be used as a the immobilized ligand.
8. ATTACHMENT OF LIGAND TO MATRIX
• Several procedures have been developed for the covalent
attachment of the ligand to the stationary phase.all procedures for
gel modification proceed in two separate chemical steps:
• 1)Activation of the functional groups on the matrix and
• 2)Joining of the ligand to the functional group on the matrix.
• A wide variety of activated gels is now commercially available.the
most widely used are described in the following:
9. •
• CYANOGEN BROMIDE-ACTIVATED AGAROSE
• This gel is especially versatile because all ligands containing primary amino groups are easily
attached to the agarose.since the gel is extremely reactive,very gentle conditions may be used to
couple the ligand.
•
•
• 6-AMINOHEXANOIC ACID(CH)-AGAROSE AND 1,6-DIAMINOHEXANE(AH)-AGAROSE
• These activated gels overcome the steric interference problems by positioning a six carbon spacer
arm between the ligand and the matrix.
• Ligands with free primary amino groups can be covalently attatched to CH-agarose,whereas ligands
with free carboxyl groups can be coupled to AH-agarose.
•
•
•
• CARBONYLDIMIDAZOLE(CDI)-ACTIVATED SUPPORTS
• Reaction with CDI produces gels that contain uncharged N-alkylcarbamate groups.
•
• EPOXY-ACTIVATED AGAROSE
• This gel provides for the attachment of ligands containing hydroxyl,thiol,or amino groups.
•
• GROUP SPECIFIC ADSORBENTS
• Group specific adsorbents contains ligands that have affinity for a class of biochemically related
substances.
• For example cibracron blue-agarose is an adsorbent which would react with enzymes that have
nucleotide cofactors(DNA Polymerase, kinase and serum albumin.)
10. EXPERIMENTAL PROCEDURE
• IS MATRIX LIGAND AVAILABLE
• NO YES
• SELECT GEL AND LIGAND SWELL GEL IN BUFFER
• COUPLE LIGAND
• PREPARE GEL FOR COLUMN
•
• PACK GEL IN GLASS COLUMN
• AND SET-UP COLUMN EQUIPMENT
•
• EQUILIBERATE COLUMN WITH BUFFER
•
• APPLY SAMPLE
•
• WASH COLUMN TO REMOVE
• UNBOUND MOLECULES
•
•
•
ELUTE BOUND MOLECULES
•
•
COLLECT AND ANALYZE ELUENT
• REGENERATE AND STORE GEL
11. • SELECTION OF A GEL OR LIGAND
• Many type of matrix-ligand systems are
commercially available and cost are reasonable
so time can be saved by purchasing preactivated
gel for direct attachment of ligand.
•
12. • BUFFER
• Buffer is used for formation of complex between a
matrix and ligand.as slight change in ionic
concentration weakens the interactions between them.
• AFFINITY ELLUTION
• In this method a selective substance added to the
buffer causes selective elution of bound
macromolecule-ligand complex.resulting in elution of
desired macromolecule.
•
• CHAOTROPIC AGENTS
• If gentle and selective elution methods do not release
the bound macromolecule then mild denaturing
agents can be added to the buffer.the most powerful
agents are urea,guanidine
13. APPLICATIONS
• 1)It is used for isolation and purification of all biological
macromolecule.
•
• 2)It is used to purify nucleic acid,antibodies,enzymes.etc
• 3)To notice which biological compounds bind to a particular
substance.
• 4)to reduce a amount of substance in a mixture
14. REFRENCES
• MODERN EXPERIMENTAL BIOCHEMISTRY-
RODNEY F. BOYER
• INTRODUCTORY PRACTICAL BIOCHEMISTRY-
S.K SWAHNEY,RANDHIR SING
