Speed of an Enzymatic Reaction

Enzymes can catalyze up to several million reactions per second. Enzyme rates depend on solution conditions and substrate concentration (Jayam et al., 2005]. The maximum speed of an enzymatic reaction is based on the substrate concentration until a constant rate of product formation. This is shown in Fig. 4.3 for indicating the saturation curve. Michaelis-Menten constant (/fm) is the substrate concentration required for an enzyme to reach... 

The speed V of an enzymatic reaction is governed by two important constants, charateristic of a given substrate the catalytic constant and the Michaelis constant... 

Catalytic antibodies - These interesting molecules are antibodies with a very specific binding site to the transition state of an enzymatic reaction. The resulting molecules, called abzymes, act like antibodies. In some cases, abzymes can speed up reaction rates as much as lO -fold over the uncatalyzed reaction. The stereospecificity of enzymes (including abzymes) may provide a tremendous aid to the synthesis of stereospecific compounds in organic chemistry. 

The choice of an appropriate electrochemical sensor is governed by several requirements (1) the nature of the substrate to be determined (ions or redox species) (2) the shape of the final sensor (microelectrodes) (3) the selectivity, sensitivity, and speed of the measurements and (4) the reliability and stability of the probe. The most frequently used sensors operate under potentiometric or amperometric modes. Amperometric enzyme electrodes, which consume a specific product of the enzymatic reaction, display an expanded linear response... 

Transamination between oxo- and amino-acids is one of the enzymatic reactions that can be duplicated in metal ion model systems (1-4). The reactive intermediates appear to be "mixed complexes in which it is thought the ligands are condensed as Schiff bases. Recently, ways of applying pH-titration techniques to these systems and analyzing the data using high speed computers have been proposed (5). This earlier study (5) which concerned the Ni(II)-pyruvate-glycinate system has been extended to an examination of the Ca(II), Mn(II) and Zn(II) systems at 25 . An attempt was also made to obtain the heats and entropies of formation of the Mn(II), Ni(Il) and Zn(II) complexes from additional titrimetric data at 10 and 40 . 

HPLC 1s carried out with a high speed chemical derivatization chromatograph (HLC 803, Toyo Soda Mfg. Co.) equipped with two detectors of ultraviolet and visible wave length, but an enzymatic reaction is performed using a Teflon tube (0.5 mm I.O. or 0.4 mn I.D. x 10,000 mm or 20,000 mm) in the thermostated water bath as shown in Fig. 1. In this equipped configuration with two detectors, elution patterns of protein and one of the lipid components can be obtained in one analysis as described in Section 2.6. 

An enzyme is a protein that speeds up a biochemical reaction without itself experiencing any overall change. In chemical language, such a compound is called a catalyst and is said to catalyze a reaction. Chemists employ a variety of compounds as laboratory catalysts, and many industrial chemical processes would be impracticably slow without catalysis. An automobile s catalytic converter makes use of a metal catalyst to accelerate conversion of toxic carbon monoxide in the exhaust to carbon dioxide. Similarly, our bodies biochemical machinery effects thousands of different reactions that would not proceed without enzymatic catalysis. Some enzymes are exquisitely specific, catalyzing only one particular reaction of a single compound. Many others have much less exacting requirements and consequently exhibit broader effects. Specific or nonspecific, enzymes can make reactions go many millions of times faster than they would without catalysis. 

Many of the important lessons of this chapter are summed up in Figure 2.11. It is not so much that enzymatic reactions are particularly fast as that uncatalyzed reactions are very slow. An enzyme is able to speed up a reaction considerably by removing some of the unfavorable features of the uncatalyzed reaction and the... 

Enzymatic ester hydrolysis is a common and widespread biochemical reaction. Since simple procedures are available to follow the kinetics of hydrolytic reactions, great efforts have been made during the last years to explain this form of catalysis in chemical terms, i.e., in analogy to known non-enzymatic reactions, and to define the components of the active sites. The ultimate aim of this research is the synthesis of an artificial enzyme with the same substrate specificity and comparable speeds of reaction as the natural catalyst. 

Equation (3) is the sum of Eq. (1) and (2). The NO2 produced by the first very rapid reaction is used up in the second rapid reaction leading to the regeneration of NO, the reactant in reaction (1). When we add reactions (1) and (2), since NO and NO2 appear on both sides of the equations, they will algebraically cancel, and the result is identical to what occurs in the absence of NO. NO is a catalyst. It enters into the reaction, speeds it up by offering an alternate pathway of lower activation energy, but is not consumed by the reaction. Reactions (1) and (2) represent a reaction mechanism, an explanation of the stoichiometry of a chemical reaction in terms of a series of elementary chemical reactions. The NO2, produced in reaction 1, and consumed in reaction (2) is called a reaction intermediate. The same scheme is involved in enzymatic catalysis, the generation of a reaction intermediate followed by the evolution of product. 

Dam-Johansen, 2010a). Membranes can be used to recover glucose (and residual ceUobiose) during the enzymatic hydrolysis to increase die reaction speed and the conversion rate. Figure 11.2 depicts the principle of glucose recovery from an enzymatic hydrolysis of cellulose via ultrafiltration. 

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