7 Key excerpts on "Enzymes as Biocatalysts"

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  eBook - ePub

  Medical Biochemistry

  • Antonio Blanco, Gustavo Blanco(Authors)
  • 2017(Publication Date)
  • Academic Press

    (Publisher)

  Countless chemical reactions take place at a given time in every living being. Many of them transform exogenous substances, which come with the diet, to obtain energy and the basic materials that will be used for the synthesis of endogenous molecules.

  Biochemical transformations are performed at a remarkable fast rate and with great efficiency. To reproduce them in the laboratory, these reactions would need extreme changes in temperature, pH, or pressure to take place; these changes are not compatible with cell survival. Under normal physiological conditions (37°C for warm-blooded organisms, pH near neutrality, and constant pressure), most of the reactions would proceed very slowly or may not occur at all. It is the presence of catalysts that allow chemical reactions in living beings to occur with great speed and under the mild conditions that are compatible with life.

  Enzymes are biological catalysts

  A catalyst is an agent capable of accelerating a chemical reaction without being part of the final products or being consumed in the process. In biological media, macromolecules called enzymes act as catalysts.

  As any catalyst, enzymes work by lowering the reaction activation energy (A e ) (see p. 152). Enzymes are more effective than most inorganic catalysts; moreover, enzymes show a greater specificity of effect. Usually inorganic catalysts function by accelerating a variety of chemical reactions, whereas enzymes catalyze only a specific chemical reaction. Some enzymes act on different substances, but generally, these are compounds with similar structural characteristics and the catalyzed reaction is always of the same type.

  The substances that are modified by enzymes are called substrates .

  The specificity of enzymes allows them to have high selectivity to distinguish among different substances and even between optical isomers of a compound. For example, glucokinase, an enzyme that catalyzes d -glucose phosphorylation, does not act on l

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  eBook - ePub

  Problem Solving in Enzyme Biocatalysis

  • Andrés Illanes, Lorena Wilson, Carlos Vera(Authors)
  • 2013(Publication Date)
  • Wiley

    (Publisher)

  1 Facts and Figures in Enzyme Biocatalysis

  1.1 Introduction

  1.1.1 Enzyme Properties

  Enzymes are the catalysts of life. Each of the chemical reactions that make up the complex metabolic networks found in all forms of life is catalyzed by an enzyme, which is the phenotypic expression of a specific gene. Thus the chemical potential of an organism is dictated by its genomic patrimony and enzymes are the biological entities that convert information into action. They are tightly regulated both by controls at the genomic level and by environmental signals that condition their mode of action once synthesized.

  Enzymes are highly evolved complex molecular structures tailored to perform a specific task with efficiency and precision. They can be conjugated with other molecules or not, but their catalytic condition resides in their protein structure. The active site—the molecular niche in which catalysis takes place—represents a very small portion of the enzyme structure (only a few amino acid residues), while the remainder of the molecule acts as a scaffold and provides necessary structural stability. Many enzymes are conjugated proteins associated with other molecules that may or may not play a role in the catalytic process. Those that do are quite important as they will determine to a great extent an enzyme's technological potential.

  “Enzyme biocatalysis” refers to the use of enzymes as biological catalysts dissociated from the cell from which they derive; the major challenge in this process is building up robust enzyme catalysts capable of performing under usually very nonphysiological conditions. The goal is to preserve the outstanding properties of enzymes as catalysts (specificity, reactivity under mild conditions) while overcoming their constraints (mostly their poor configurational stability). The pros and cons of enzymes as catalysts are thus the consequence of their complex molecular structure. Enzymes are labile catalysts, with enzyme stabilization being a major issue in biocatalysis and a prerequisite for most of their applications. Several enzyme stabilization strategies have been proposed, including: searching for new enzymes in the biota and metagenomic pools [1], improving natural enzymes via site-directed mutagenesis [2] and directed evolution [3], catalyst engineering (chemical modification [4], immobilization to solid matrices [5], and auto-aggregation [6]), medium engineering (use of nonconventional reaction media) [7], and, most recently, reactivating enzymes following activity exhaustion [8]. Enzyme immobilization has been a major breakthrough in biocatalysis and has widened its field of application considerably [9].

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  eBook - ePub

  Biotechnology for Beginners

  • Reinhard Renneberg, Vanya Loroch(Authors)
  • 2016(Publication Date)
  • Academic Press

    (Publisher)

  biological catalysts —turning substances into other products without undergoing any change themselves.

  Due to enzymes, chemical reactions reach their equilibrium much faster and may be speeded up by a factor of up to 10 12 . It is the activity of enzymes that makes life possible at all. Turning sugar into alcohol and carbon dioxide is a matter of seconds for the enzymes in yeast cells, but without them it would take hundreds of years and be virtually impossible. Enzymes are highly effective, high-performing biocatalysts .

  In cells ranging in size between a tenth and a thousandth of a millimeter, thousands of coordinated enzymatic reactions take place every second (See Figs. 4.5 and 4.6 in Chapter 4 ).

  This can only work because each of the molecular catalysts involved recognizes its specific substrate among thousands of other compounds within a cell and turns it to a specific product. This process, called biocatalysis, takes place in the active site of the enzyme.

  Nearly all biological catalysts are proteins. However, RNA (ribonucleic acid) can also act as a biocatalyst (see Chapter: The Wonders of Gene Technology ). These ribozymes often break down other RNA molecules. RNA can also be used to build artificial aptamers that bind to designated compounds (see Chapter: Analytical Biotechnology and the Human Genome ).

  As early as 1894, the German chemist Emil Fischer (1852–1919), who was later awarded the Nobel Prize (Fig. 2.4 ), postulated that enzymes recognize their substrates on a lock-and-key principle . If the active site of an enzyme lies in a dimple (cavity, crevice) on the molecule’s surface, the substrate molecule must fit accurately, just like a key into its lock. Even slightly modified molecules will no longer interact with the enzyme. Lock-and-key is a viable preliminary explanation for the high substrate specificity of enzymes. It also explains why the shape of competing enzyme inhibitors (e.g., penicillin) strongly resembles that of the original substrate. Like a skeleton key, they block the active site of an enzyme (competitive inhibition

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  eBook - ePub

  Chemistry of Biomolecules, Second Edition

  • S. P. Bhutani(Author)
  • 2019(Publication Date)
  • CRC Press

    (Publisher)

  Enzymes are soluble in water and work in aqueous solution in living cells. They are sometimes described as organic catalysts. A catalyst is a substance which accelerates the rate of a chemical reaction. Many of the biochemical reactions catalysed by enzymes are reversible reactions. An example of a reversible reaction is given below:

  At equilibrium the rate at which A and B are converted to C may or may not be equal to the rate at which C is converted back to A and B. The position of equilibrium depends on the energy difference betwen the reactants and product (Fig. 3.16 ).

  Fig. 3.16 Activation energy profile for a typical reaction.

  Enzymes, like all catalysts, speed up reactions but they cannot alter the equilibrium constant or the free energy change. The reaction rate depends on the free energy of activation or activation energy i.e., the energy required to initiate the reaction. The activation energy for an uncatalysed reaction is higher than that for a catalysed reaction. That means an uncatalysed reaction requires more energy to get started than that required for a catalysed reaction (Fig. 3.17 ).

  Enzymes do not alter the direction of a reaction; they speed up the rate at which equilibrium is reached. In doing so, they can catalyse reversible reactions in either direction provided it is energetically feasible.

  Biochemical reactions involve the formation or the destruction of chemical bonds. When two or more reactants are joined, chemical bonds are formed. When a complex molecule is split into simpler components, chemical bonds are destroyed. In both the cases, energy is required to bring about the changes. That energy is the activation energy. Heat can be used as a source of activation energy. Many chemical reactions do not proceed quickly unless the reactants are raised to relatively high temperatures. In living cells, however, reactions take place rapidly at relatively low temperatures. Enzymes lower the amount of activation energy needed, making it possible for reactions to occur at temperatures which are otherwise energetically unfavourable.

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  eBook - ePub

  Pharmaceutical Biotechnology

  A Focus on Industrial Application

  • Adalberto Pessoa, Michele Vitolo, Paul Frederick Long, Adalberto Pessoa, Michele Vitolo, Paul Frederick Long(Authors)
  • 2021(Publication Date)
  • CRC Press

    (Publisher)

  Enzymes are catalytic proteins capable to convert a compound (substrate) to another (product) at high reaction rate. In enzyme-catalyzed reactions, enzymes, in general, specifically accept only one substrate. Even when an enzyme catalyzes the conversion of more than one substrate, the reaction rates are different. Substrate specificity is linked to a region of the enzyme molecule called the active site, which can be envisaged as a rigid or flexible structure depending on the particular reaction considered. Currently, it is considered that the active site is organized into two sub-regions. At one of them, the substrate fitting occurs (the so-called bonding site), and in the other, the chemical transformation of the substrate occurs (the so-called catalytic site). Generally, it can be considered that an enzyme-catalyzed reaction proceeds through three different steps: first step (period in which the enzyme and substrate are mixed into the reaction medium. The enzyme-substrate complex is formed and accumulates); second step (a period during which the concentration of the ES complex remains constant in the reaction medium, the substrate concentration diminishes, and the product concentration increases); third step (the concentration of the ES complex in the reaction medium is not constant; the consumption of substrate and formation of product occur more slowly). The fundamental aspect is that the catalysis rate and substrate concentration follow a hyperbolic correlation. The enzyme activity can be affected by factors of different nature, i.e., physical-chemical factors (pH, temperature, ionic strength, water activity, etc.), chemical factors (activators, inhibitors –irreversible or reversible (competitive, non-competitive and uncompetitive) –, stabilizers, and deactivators) and physical factors (pressure and shear forces). The ability to quantify enzyme activity is essential if an enzyme is to be used in a cost-effective way in an industrial process or other analytical methods. Focusing on industrial processes, some considerations must be made in order to evaluate the suitability using enzymes as catalysts in specific reactions. The basic considerations should be: (a) the amount of enzyme necessary; (b) the duration of the reaction; (c) the initial substrate concentration necessary; (d) the reaction conditions; and (e) the cost involved. In general, the effective cost of an enzymatic process derivates from the ratio between the additional cost due to the enzyme and the improvement of the process yield and/or the aggregate value of the final product, taking into consideration the economic cost of the overall process.

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  Bioprocess Engineering

  An Introductory Engineering and Life Science Approach

  • Kim Gail Clarke(Author)
  • 2013(Publication Date)
  • Woodhead Publishing

    (Publisher)

  6 Enzymes as Biocatalysts Abstract: Every biochemical reaction in the cell is catalysed by specific enzymes. Enzymes function in the same manner as do chemical catalysts, namely to lower the activation energy. Isolation of enzymes, either in a crude or purified form, permits biotransformation directly without the need for whole cells. In fact, biotransformations with isolated enzymes rather than cells as biocatalysts confer several advantages. High selectivity can be obtained with enzyme biocatalysts, because fewer by-products are produced, and many enzymes confer high degrees of regioselectivity. By far the most common enzymes utilised in enzyme engineering to date have been extracellular and almost exclusively hydrolytic. These are relatively simple to extract and require little in the way of purification (Section 11.4). Even today, amylases 1 and proteases 2 are widely used in the food and beverage and detergent industries respectively. Probably the first intracellular enzyme to be used was glucose isomerase. This was mainly used in conjunction with amylase in the production of high fructose sweet syrups and jams from starch. Isomerisation of the glucose (produced from the hydrolysis of starch by amylase) produced fructose, which, with its 1.5-fold sweetening power compared with glucose, provided a correspondingly sweeter syrup for the same quantity of starch. The first major usage of an enzyme other than that for food or detergents was penicillin amidase. Penicillin amidase, which catalyses the formation of 6-amino penicillanic acid, the precursor of synthetic penicillin, heralded the start of the synthetic pharmaceutical industry. Today the use of Enzymes as Biocatalysts is widespread in diverse industries, with advances in genetic engineering contributing significantly to the pool of enzymes available

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  Biochemistry

  • Raymond S. Ochs(Author)
  • 2021(Publication Date)
  • CRC Press

    (Publisher)

  6 Enzymes

  The word enzyme is German for in yeast. Near the end of the 19th century, the demonstration that a cell-free extract could cause sugar to ferment – as dramatically demonstrated by the formation of bubbles of CO2 – was a blow to the vitalist theory that only intact cells could carry out biological reactions. The extract was named zymase; today, we use the word enzyme to describe a catalyst involved in one reaction.

  A catalyst causes an increase in the rate of a reaction without affecting its equilibrium position. To visualize the action of an enzyme, consider placing weights on a dual-pan balance (Figure 6.1 ). If weights are dropped onto both pans, they will oscillate until they settle into their final equilibrium rest positions. If you intercede in this process just after the weights are dropped using your hands as dampeners, the time needed to reach the final state is much shorter. Yet the heights of the pans in their final equilibrium (rest) positions are unaffected by this intervention. The steadying hands represent the action of an enzyme, which increases the rate of approach to equilibrium (the rate of a reaction in both forward and reverse directions) but does not affect the final state of equilibrium. An intriguing corollary is that an enzyme has no effect on a reaction at equilibrium. Thus, the study of enzyme kinetics is that of the time course approaching, but not having reached, equilibrium.

  FIGURE 6.1 Equilibrium balance. A dual-pan balance models equilibrium. (a) Weights are dropped on the balance, and (b) it oscillates about its true end state. (c) A pair of hands steadies the balance, and (d) it achieves an equilibrium point, which is the same point that it would reach without the hands in (d). The hands symbolize enzyme action.

  6.1 Energetics of Enzyme-Catalyzed Reactions

  In any reaction, converting substrate to product requires intermediate states. Those intermediates are always less stable – and thus of higher energy – than either the substrate or the product. In the simplest theoretical case of one intermediate, we can speak of the transition state, although invariably more than one exists. The difference in energy level between the substrate and the transition state is called the activation energy

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