Enzyme semisynthetic

In another approach the specificity of an existing enzyme has been changed. Levine and Kaiser (57) have transformed a protease, papain, into a redox enzyme by alkylation of the active site thiol with (27), a derivative of xanthine. 

The enzyme termed flavopapain, reacts with dihydronicotinamides. The catalyst exhibits saturation kinetics and modest rate enhancements over appropriate model compounds. 

Many of the basic elements of enzyme catalysis have been illustrated here, including binding of substrate, multifunctional catalysis, microenvironmental effects, covalent catalysis, and strain effects. The most remarkable rate enhancements reported to date are those brought about by apolar derivatives of PEI, a polycation. These rate enhancements are very en- 

As stated earlier, to make such a catalytic center is not a simple job. However, it can be said with confidence that, in view of the successes with some of the structures described here, the goal appears a great deal more attainable now than it was two decades ago when Morawetz, Bender, Bruice, and others began looking at enzyme models. 

Bender, M. L., Mechanisms of Homogeneous Catalysis from Protons to Proteins, p. 281. Wiley, New York, 1971. 

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The application of CPO, HRP and CiP is limited to sterically unencumbered substrates and all these peroxidases produce the same absolute configuration of the chiral hydroperoxide. To overcome this limitation, the semisynthetic enzyme selenosubtilisin, a mimic for glutathione peroxidase, with the peptide framework of the serine protease subtilisin was developed by Bell and Hilvert. This semisynthetic peroxidase catalyzes the reduction of hydrogen peroxide and hydroperoxides in the presence of 5-mercapto-2-nitrobenzoic acid. It was utilized by Adam and coworkers and Schreier and coworkers for the kinetic resolution of racemic hydroperoxides (equation 17) . The results obtained were very promising. 

One of the major disadvantages of utilizing enzymes or semisynthetic enzymes for chemical transformations is the fact that large quantities of pure enzyme are needed for preparative scale. This disadvantage is contrasted with whole cell systems (bacteria, fungi, plant/animal cells) because they are easily available in large quantities through... 

In our initial research on semisynthetic enzymes, we examined briefly the modification of the serine proteinase a-chymotrypsin, perhaps the best understood of the proteolytic enzymes. A logical choice as a residue for alkylation in the active site of a-chymotrypsin is His-57. However, an examination of a three-dimensional model (Lab Quip) of chymotrypsin in which coenzyme analogs were covalently attached to His-57 suggested strongly that such modifications would block completely the enzyme s active site region and that the probability of new reactions being catalyzed by the modified enzyme would be low. Another possible site of modification of chymotrypsin that could be considered was Met-192. This residue, located on the periphery of the... 

Ideally, one would like to be able to generate a unique active site for any chemical transformation. However, the number of structurally well-characterized proteins for construction of semisynthetic enzymes is limited. An alternative approach exploits the mammalian immune system to produce binding pockets that are specifically tailored to the reaction of interest. 

Haring D, Schueler E, Adam W, Saha-Moeller CR, Schreier P. Semisynthetic enzymes in asynunetric synthesis enantioselec-tive reduction of racemic hydroperoxides catalyzed by seleno-subtilisin. J. Org. Chem. 1999 64 832-835. 

With few exceptions, enzymatic processes in carbohydrates cause degradation. Enzymes are used in the form of pure or semipure preparations or together with their producers, i.e., microorganisms. Currently, semisynthetic enzymes are also in use. Alcoholic fermentation is the most common method of utilization of monosaccharides, sucrose, and some polysaccharides, e.g., starch. Lactic acid fermentation is another important enzymatic process. Lactic acid bacteria metabolize mono- and disaccharides into lactic acid. This acid has a chiral center thus either D(-), L(+), or racemic products can be formed. In the human organism, only the L(+) enantiomer is metabolized, whereas the D(-) enantiomer is concentrated in blood and excreted with urine. Among lactic acid bacteria, only Streptococcus shows specificity in the formation of particular enantiomers, and only the L(+) enantiomer is produced. 

Arnold U et al (2002) Protein prosthesis a semisynthetic enzyme with a beta-peptide reverse turn. J Am Chem Soc 124(29) 8522-8523... 

T. Nakatsuka, T. Sasaki, E.T. Kaiser, Peptide segment coupling catalyzed by the semisynthetic enzyme thiolsubtilisin, J. Am. Chem. Soc. 1987, 109, 3808. 

Recently Keyes (80-82) described an interesting approach to the synthesis of semisynthetic enzymes. A protein was partially denaturated and then brought in contact with an inhibitor of an enzyme to be modelled. 

Semisynthetic enzymes will have to be prepared and compared for their activity and need to be spectroscopically characterized. The requirements for models in a biological environment are high with respect to stability and solubility another challenge for the bioinorganic chemist. 

Hamachi. 1. Watanabe. J. Eboshi. R. Fliraoka. T. Shinkai, S. Incorporation of artificial receptors into a protein/peptide surface A strategy for on/off type of switching of semisynthetic enzymes. Biopolymers 2000, 55 (6). 459-468. 

In 1977, Kaiser and coworkers introduced the concept of semisynthetic enzymes whereby an existing enzyme is modified by selective and covalent attachment of coenzyme analogs to one of the amino acid residues at its binding site [63-65]. 

Chemically Modified Enzymes. Besides varying the physicochemical properties of enzymes (such as their solubility), the catalytic properties of an enzyme can be fundamentally altered by chemical modification of the chemical operator in the active site. This teclmique leads to semisynthetic enzymes, which often do not have much in conunon with their natural ancestors [492, 493]. Early efforts in this directiOTi focussed on the modification of nucleophilic OH- or SH-residues in Ser-or Cys-hydrolases, such as subtihsin or papain, respectively. For example, the Ser-hydroxy group within the active site of subtilisin was converted to its selenium... 

Sih CJ, Chen C-S (1984) Microbial asymmetric catalysis - Enantio-selective reduction of ketones. Angew Chem Int Ed Engl 23 570-578 Slama J, Oruganti SR, Kaiser ET (1981) Semisynthetic enzymes Synthesis of a new flavopapain with high catalytic efficiency. J Am Chem Soc 103 6211-6213... 

Slama JT, Radziejewski C, Oruganti SR, Kaiser ET (1984) Semisynthetic enzymes Characterization of isomeric flavopapains with widely different catalytic efficiencies. J Am Chem Soc 106 6778-6785 Srinivasan R, Medary RT, Fisher HF, Norris DJ, Stewart R (1982) The pyridinium-dihydropyridine system. Reduction potentials and the mechanism of oxidation of 1,4-dihydropyridines by a Schiff base. J Am Chem Soc 104 807-812... 

Semisynthetic Enzymes. Enzymes that are modified by chemical means are known as semisynthetic enzymes. There are two main ways to produce semisynthetic enzymes atom replacement or group attachment. 

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