Enzymes — artificial modification

The powerful tool of molecular genetics allows the modification of each single amino add in the peptide chain of a protein, e.g. ddetion of side residues necessary for isoprenylation or palmitoylation1361 or introduction of additional charged amino acids for electrostatic interaction with the plasma membrane.1371 Even some artificial modifications can be introduced by means of recombinant enzymes as shown above. 

Mbs (Fig. 16), in which almost all studies have focused on the interaction between the artificial hemes and the protein matrix or the physiological function of Mb. In contrast, there has been a limited number of extensive studies that demonstrate the modification of Mb to provide new and useful functions (72). In the following sections, the conversion of Mb into unique heme enzymes by replacement of the native hemin with an artificially created prosthetic group is described. 

Semi-synthetic enzymes are produced by the reconstitution of apo-proteins with artificial active sites that yield novel catalytic functions [237]. For example, reconstitution of apo-myoglobin with Co(II)-protoporphyrin IX results in a novel biocatalyst that is capable of hydrogenating acetylene derivatives or evolving hydrogen [209, 238]. By the modification of the reconstitution of apo-proteins with artificial redox-active cofactors and the covalent attachment of photosensitizer units, photo-... 

Human insulin (1980) is made either by enzyme modification of porcine insulin, or by using recombinant DNA to synthesise the proinsulin, precursor molecule for insulin. This is done by artificially introducing the DNA into either Escherichia coli or yeast. 

The presence of a number of enzyme-recognizable amino acid residues, such as glutamine residues in the case of TGase, restricts the site-specific introduction of glycans. When the target protein has many glutamine residues, site specific modification can not be performed artificially. The introduction of an unnatural amino acid, however, allows the exact glycosyla-tion site to be determined. 

D Souza VT (2003) Modification of cyclodextrins for use as artificial enzymes. Supramol Chem 15 221-229... 

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