Biochemical catalytic production enzymes

To form catalytically productive enzyme/substrate complexes, many peptide bond cis-trans isomerases essentially require the location of the reactive bond of the substrate in the context of secondary binding sites or a specific spatial organization of the polypeptide chain thus creating features of stereo- and regiospecifi-city [19,20]. As in the case of many endoproteases, PPIases can utilize an extended array of catalytic subsites to enhance catalytic efficiency and substrate specificity. These properties precondition peptide bond cis-trans isomerases toward a complex reaction pattern. Consequently, biochemical investigations have led to the elucidation of three distinct molecular mechanisms that might be operative either in isolation or collectively in the cellular action of both prototypical and multidomain peptide bond cis-trans isomerases ... 

In terms of biodiesel conversion processes, chemical conversion using alkali and acid-based catalysts is stiU the most favorite approach. Various investigations have been carried out to develop novel catalysts and/or novel processes for efficient conversion of TAG to FAME. This part was reviewed in the chapter Production of biodiesel via catalytic upgrading refining of sustainable oleageneous feedstocks. The chapter Biochemical catalytic production of biodiesel introduced a promising alternative way of biodiesel production via enzyme-catalyzed processes. Recentiy, microalgae... 

Finally, for an overall perspective on catalysis of all types, here are a few words about biochemical catalysts, namely, enzymes. In terms of activity, selectivity, and scope, enzymes score very high. A large number of reactions are catalyzed very efficiently, and the selectivity is high. For chiral products enzymes routinely give 100% enantioselectivity. However, large-scale application of enzyme catalysis in the near future is unlikely for many reasons. Isolation of a reasonable quantity of pure enzyme is often very difficult and expensive. Most enzymes are fragile and have poor thermal stability. Separation of the enzyme after the reaction is also a difficult problem. However, in the near future, catalytic processes based on thermostable enzymes may be adopted for selected products. 

Enzymes are catalytically active proteins that are involved in every in vivo transformation. They enhance the rates of biochemical reactions by 10 to 10 2 by reduction of the free energy of activation. Two distinctive properties of enzymes are their high substrate specificity and the narrow range of conditions under which they are effective. They usually catalyze one reaction of a few substrates. Activities are dependent on pH, temperature, the presence of cofactors, as well as concentrations of substrates and products. Enzymes perform specific reactions because they possess cavities in which substrates are oriented white they are transformed (Figure 1). This process involves interaction of the substrate with amino acids of the enzyme. 

However valuable kinetic studies are, they reveal little about how enzymes catalyze biochemical reactions. Biochemists use other techniques to investigate the catalytic mechanisms of enzymes. (A mechanism is a set of steps in a chemical reaction by which a substrate is changed into a product.) Enzyme mechanism investigations seek to relate enzyme activity to the structure and function of the active site. X-ray crystallography, chemical inactivation of active site side chains, and studies using simple model compounds as substrates and as inhibitors are used. 

This chapter is an overview of architectures adopted for the catalytic/biocatalytic composites used in wide applications like the biomass valorization or fine chemical industry. On this perspective, the chapter updates the reader with the most fresh examples of construction designs and concepts considered for the synthesis of such composites. Their catalytic properties result from the introduction of catalytic functionalities and vary from inorganic metal species e.g., Ru, Ir, Pd, or Rh) to well-organized biochemical structures like enzymes e.g., lipase, peroxidase, (3-galactosidase) or whole cells. Catalytic/biocatalytic procedures for the biomass conversion into platform molecules e.g., glucose, GVL, Me-THF, sorbitol, succinic acid, and glycerol) and their further transformation into value-added products are detailed in order to make understandable the utility of these complex architectures and to associate the composite properties to their performances, versatility, and robustness. 

Biochemical industries are based on the growth of microbes such as bacteria, fungi, molds, yeasts and others. Although some microbes are grown as food, interest here is in the production of chemicals with their aid. A distinction is drawn between steps that involve cells and those that employ isolated catalytic enzymes which are metabolic products of cells. Major characteristics of microbial processes that may be contrasted with those of ordinary chemical processing include the following ... 

Different from conventional chemical kinetics, the rates in biochemical reactions networks are usually saturable hyperbolic functions. For an increasing substrate concentration, the rate increases only up to a maximal rate Vm, determined by the turnover number fccat = k2 and the total amount of enzyme Ej. The turnover number ca( measures the number of catalytic events per seconds per enzyme, which can be more than 1000 substrate molecules per second for a large number of enzymes. The constant Km is a measure of the affinity of the enzyme for the substrate, and corresponds to the concentration of S at which the reaction rate equals half the maximal rate. For S most active sites are not occupied. For S >> Km, there is an excess of substrate, that is, the active sites of the enzymes are saturated with substrate. The ratio kc.AJ Km is a measure for the efficiency of an enzyme. In the extreme case, almost every collision between substrate and enzyme leads to product formation (low Km, high fccat). In this case the enzyme is limited by diffusion only, with an upper limit of cat /Km 108 — 109M. v 1. The ratio kc.MJKm can be used to test the rapid... 

Despite the large amount of biochemical and structural studies of sirtuins in complex with various substrates, cofactors and reaction products, the catalytic mechanism of this class of enzymes is still a matter of debate. SN -like [56] and SN -like [60] mechanisms have been inferred from structural studies but further biochemical and possibly structural studies will be required to clarify which mechanism is used by sirtuins. It should also be noted that another matter of debate concerns the mode of noncompetitive inhibition of sirtuins by the reaction product nicotinamide [62], various structural studies having highlighted different binding pockets for this molecule [63, 64]. 

Microbial cells contain or produce at least 2500 different enzymes which can catalyze biochemical reactions leading to growth, respiration and product formation. Most of these enzymes can readily be separated from cells and can display their catalytic activities independently of the cells. Although microbial enzyme activities have been observed for many centuries, only recently have microbial enzymes been commercially utilized. 

The crystal stmctures of snbstrate-rednced amine oxidases have been solved, along with site-directed mutants, metal-snbstitnted forms, enzyme complexes with inhibitors, the Oi mimic nitric oxide (NQ) and peroxide. These have been correlated with a wealth of biochemical and spectroscopic data that form the basis for the catalytic mechanism proposed in Scheme 8. A Schiffbase complex species (b) is formed between snbstrate amine and TPQ C-5. Base-catalyzed proton abstraction from substrate a-methylene group, via the conserved active-site aspartate residue, yields the reduced cofactor in a product Schiff-base complex, species (c). Hydrolysis releases product aldehyde, leaving the cofactor in the reduced aminoquinol form, species (d). 

The catalytic mechanism of Icmt is proposed to be an ordered bi-bi kinetic reaction [38,39]. In this mechanism, the methyl donor, SAM, binds to the active site first, followed by binding of the prenylcysteine substrate. Once the transfer reaction is complete, the methylated product is released followed by dissociation of 5-adenosyl-L-homocysteine (AdoHcy, SAH). Further biochemical and biophysical experiments are underway to further elucidate the mechanism of methyl donor and acceptor binding and catalysis of these unique enzymes. 

---