Biocatalysts peptide catalysts

Synthesis chemists were very inventive when they were developing effective peptide catalysts simulating definite properties of modeled enzymes. Despite a series of successful syntheses of biomimics, their action rate and selectivity were much worse than those of natural biocatalysts. 

An enzyme, the most typical biocatalyst, is a protein (or peptide molecular chain), which can be made from living cells and promote, direct or facilitate the occurrence of a specific chemical reaction, without being consumed during the course of such reaction. The term enzyme is mostly used to describe proteinaeceous catalysts. However, in some instances it also includes co-enzymes or co-factors as they are supposed to be required to bring about the desired reaction. 

Despite their good catalytic properties, proteases are not ideal catalysts for the synthesis of peptides. Its specificity and selectivity might limit their potential, particularly in the case of rather large peptides where unwanted hydrolytic reactions will occur over the formed product and the substrates. Besides, the use of non-conventional reaction media and the conditions of temperature and pH required for synthesis can be detrimental both for protease activity and stability (Barberis et al. 2002 Bordusa 2002 Quiroga et al. 2005, 2006). However, there are different strategies to overcome such problems, which comprise the engineering of the reaction medium, the biocatalyst and the substrate (Lombard et al. 2005). 

Alternatively, enzymes, which are biocatalysts, have many favorable properties compared to conventional chemical catalysts. Enzymes are large proteins that are made up of a sequence of 20 natmaUy occurring amino add residues to form a chain connected by peptide bonds, shown in Figure 1.2. As with chemical catalysts, enzymes alter the reaction by providing different pathways and operate effectively in small amounts (Lorenz and Eck, 2005). It has been reported that enzymes... 

Organisms do not use single amino acids as biocatalysts, but rather macromolecules comprised of them - enzymes - with nearly perfect selectivities in the functions they perform. But already the combination of just two amino acids to a dipeptide often creates a much better catalyst for the synthesis of caibohydiates under aqueous conditions (45, 46). Alanine for example catalyses the formation of erythrose with 7% ee (44) and the dipeptide L-Ala-L-Ala with 33% ee (46). How exactly peptides evolved under prebiotic conditions is another topic of debate as peptide formation from amino acids in water is thermodynamically not favored, requiring special conditions and activations (47). 

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