Bioaffinity Based Immobilization of Enzymes - Advances in Biochemical Engineering Biotechnology - page 210

2.6
Utility in Organic Solvents
The potential of enzyme action in organic solvents is now well recognized. Some
enzymes have been shown not only to retain their catalytic function but also to
catalyze novel reactions and exhibit remarkable stability in organic solvents [2].
The significance of support matrices for the utilization of enzymes in organic
solvents has been recognized [96] and proteinic supports may be particularly
useful [97]. While no detailed study on the behaviour of enzymes immobilized
on antibody support in organic solvents has been,to my knowledge,reported,
antibodies seem to retain their affinity at least for haptens. Russel et al. [98]
demonstrated that the binding and specificity of the hapten 4-aminobiphenyl
for the immobilized monoclonal antibody 2E-is retained in several non-aqueous
media but the interaction was found to be inversely related to the hydrophobici-
ty of the solvent. Similarly the monoclonal antibody 8 H 11,that binds to the
pesticide aldrin,coupled to a large molecular weight carbohydrate support
retained its ability bind the pesticide albeit with lowered affinity in organic sol-
vent for 5 h; over 90,60 and 57 % binding was retained in acetonitrile,methanol
and 2 propanol respectively [99]. In an earlier interesting study Janda et al. [100]
observed that immobilization on porous glass conferred additional stability to
lipase like catalytic monoclonal antibody in organic solvents.
3
Lectin Affinity Based Immobilization of Glycoenzymes
Lectins and glycoenzymes represent the second bioaffinity pair with proven
potential in the immobilization of the later. Glycosylation is the most common
post-translational modification encountered in eucaryotes,archaebacteria and
even some procaryotes [40] and a large number of enzymes are glycosylated
to varying extent [40]. Several enzymes being currently used in industry and
analysis are glycoproteinic [101].
To date hundreds of lectins have been isolated from plants,microorganisms
and animals. In spite of some common biological properties that lead to assign-
ment of majority of lectins to distinct families of homologous proteins,lectins
and their sugar recognizing/combining sites may be structurally diverse [102].
The largest and best characterized among the lectins is Con A belonging to the
legume family. Con A has been widely used in the affinity purification of a
variety of glycoenzymes and nearly exclusively in the immobilization of
glycoenzymes on a variety of supports. Work on the utility of Con A in glyco-
enzyme immobilization has been recently reviewed [103].
3.1
Concanavalin A
Con A is a non-glycosylated oligomeric protein that exists as tetramer above
pH 7.0 but dissociates to dimers below pH 6.0. Each monomer is 237 amino acids
long and has sites for binding of a transition metal ions and a calcium ion in