Michaelis kinetics

It must be pointed out that Michaelis kinetics does not apply in the presence of acceptors. Constants like apparent ymax, KM, and K are dependent on acceptor concentrations. In order to understand the reactions occurring in the presence of different types of acceptors, and to provide an appropriate background for reaction engineering in industrial processes, the kinetics of the different reaction pathways... 

Non-Michaelis kinetics observed. Value for defined where rate = Vaax- M Mittler and Zilinskas, 1991b. 

This picture is also valid for many homogeneous catalysts, too, in particular hydrogen and hydroxyl ions, and for heterogeneous catalysts, since one may, on the Langmuir picture, equate the chemisorbed species as an intermediate complex between site and substrate. The Michaelis kinetics, viz.. 

The reduction of retinaldehyde to retinol was studied with an approximately 13-fold purified soluble enzyme preparation from rat intestinal mucosa (Fidge and Goodman, 1968). The enzyme was relatively heat stable and had a molecular weight approximately in the range of 60,000-80,000. The partly purified reductase was unable to oxidize ethanol in the presence of NAD" ". Retinaldehyde reduction required NADH or NADPH as cofactor both reduced nucleotides were effective. The reaction was stimulated by glutathione and inhibited by thiol inhibitors. There was a sharp pH optimum near 6.3. Retinaldehyde reduction displayed typical Michaelis kinetics, with a 2 xmol of retinol formed per... 

Arylsulphatase A (pH optimum 4.8) from bovine liver hydrolysed L-ascorbic acid 2-sulphate Michaelis kinetics Km 21 mmol 1 ) were obeyed at pH 5.6, but not at pH 4.8. Potassium sulphate is a competitive inhibitor of the enzyme (ATi 0.2 and 0.6 mmol 1 at pH 4.8 and 5.6, respectively), which is converted into a substrate-modified form during the reaction. The corresponding arylsulphatase B also hydrolysed L-ascorbic acid 2-sulphate Km 8 (xmol 1 ), but the activity was appreciably decreased in the absence of sodium chloride the enzyme was also competitively inhibited by potassium sulphate K 0.1 mmol 1 ). Arylsulphatases from the mollusc Dicathais orbita and from Aerobacter aerogenes did not hydrolyse L-ascorbic acid 2-sulphate. 

The enzyme catalyzing the condensation of two molecules of 5-AL to one of PBG (Fig. 11) is widely distributed in animal tissues (72-75), and the use of 5-AL in porphyrin biosynthesis has been shown in spinach (74), yeast (74), and bacteria (59, 74, 76). The preparation from ox liver (74) and that from rabbit reticulocytes (75) have been considerably purified and show very similar characteristics. The enzyme from ox liver is rather specific for its substrate. 2,5-Diamino-4-ketopentanoic acid, 6-amino-5-ketohexanoic acid, and aminoacetone form no pyrrole with this enzyme, and are only weakly inhibitory if at all. The rabbit enzyme does not act on amino acetone, nor does it seem to form a mixed pyrrole in the presence of both 5-AL and aminoacetone. The kinetics of this enzyme are of interest since it is a rare case of an enzyme catalyzing a reaction between two identical. substrate molecules. Both the rabbit and ox liver enzymes follow simple Michaelis kinetics over the range 10 to 2 X M substrate concentration. The simplest interpretation of these data, together with some related chemical evidence (75), is that the enzyme binds both molecules of substrate specifically, the first more tightly than the second. In this respect it resembles most the enzyme-coenzyme substrate reactions. The reaction... 

Michaelis kinetics (Michaelis-Menten kinetics) A simple and useful model of the kinetics of enzyme-catalyzed reactions. It assumes the formation of a specific enzyme-substrate complex. Many enzymes obey Michaelis kinetics and a plot of reaction velocity (V) against substrate concentration [S] gives a characteristic curve showing that the rate increases quickly at first and then levels off to a maximum value. When substrate concentration is low, the rate of reaction is almost proportional to substrate concentration. When substrate concentration is high, the rate is at a maximum, V iax) independent of substrate concentration. The Michaelis constant is the concentration of substrate at half the maximum rate and can be determined experimentally by measuring reaction rate at varying substrate concentrations. Different types of inhibition can also be distinguished in this way. Allosteric enzymes do not obey Michaelis kinetics. 

Fig. 1. Free-energy profile for a kinetic resolution depicted by equation 1 that follows Michaelis-Menten kinetics.

Leonor Michaelis and Maud Menten laid the foundation for enzyme kinetics as early as 1913 by proposing the following scheme ... 

Figure 11-1a. Simple Michaelis-Menten kinetics. At low substrate concentration...

The Michaelis constant is equal to substrate concentration at which the rate of reaction is equal to one-half the maximum rate. The parameters and characterize the enzymatic reactions that are described by Michaelis-Menten kinetics. is dependent on total... 

Equation 11-15 is known as the Michaelis-Menten equation. It represents the kinetics of many simple enzyme-catalyzed reactions, which involve a single substrate. The interpretation of as an equilibrium constant is not universally valid, since the assumption that the reversible reaction as a fast equilibrium process often does not apply. 

The Michaelis-Menten Equation 11-15 is not well suited for estimation of the kinetic parameters and Reananging Equation 11-15 gives various options for plotting and estimating the parameters. 

Michaelis-Menten kinetics Kineties of eonversion of substrates in enzyme-eatalyzed reaetions. 

The kinetic expressions arehighlynonlinearbecause they include a Michaelis-Menton rate term ... 

Saturation kinetics are also called zero-order kinetics or Michaelis-Menten kinetics. The Michaelis-Menten equation is mainly used to characterize the interactions of enzymes and substrates, but it is also widely applied to characterize the elimination of chemical compounds from the body. The substrate concentration that produces half-maximal velocity of an enzymatic reaction, termed value or Michaelis constant, can be determined experimentally by graphing r/, as a function of substrate concentration, [S]. 

The Michaelis-Menten equation is, like Eq. (3-146), a rectangular hyperbola, and it can be cast into three linear plotting forms. The double-reciprocal form, Eq. (3-152), is called the Lineweaver-Burk plot in enzyme kinetics. ... 

Lenore Michaelis and Maud L. Menten proposed a general theory of enzyme action in 1913 consistent with observed enzyme kinetics. Their theory was based on the assumption that the enzyme, E, and its substrate, S, associate reversibly to form an enzyme-substrate complex, ES ... 

If the kinetics of the reaction disobey the Michaelis-Menten equation, the violation is revealed by a departure from linearity in these straight-line graphs. We shall see in the next chapter that such deviations from linearity are characteristic of the kinetics of regulatory enzymes known as allosteric enzymes. Such regulatory enzymes are very important in the overall control of metabolic pathways. 

Smith, W. G., 1992. In kinetics and the reversible Michaelis-Menten model. Journal of Chemical Education 12 981 — 984. 

FIGURE 15.8 Sigmoid versus [S] plot. The dotted line represents the hyperbolic plot characteristic of normal Michaelis-Men ten-type enzyme kinetics. 

On the other hand, for an enzyme that obeys Michaelis-Menten kinetics, the reaction is viewed as being first-order in S at low S and zero-order in S at high S. (See Chapter 14, where this distinction is discussed.)... 

Each of the processes shown in Figure 2.8 can be described by a Michaelis-Menten type of biochemical reaction, a standard generalized mathematical equation describing the interaction of a substrate with an enzyme. Michaelis and Men ten realized in 1913 that the kinetics of enzyme reactions differed from the kinetics of conventional... 

As with the Langmuir adsorption isotherm, which in shape closely resembles Michaelis-Menten type biochemical kinetics, the two notable features of such reactions are the location parameter of the curve along the concentration axis (the value of Km or the magnitude of the coupling efficiency factor) and the maximal rate of the reaction (Vmax). In generic terms, Michaelis-Menten reactions can be written in the form... 

Michaelis-Menten kinetics, in 1913 L. Michaelis and M. Men ten realized that the rate of an enzymatic reaction... 

Most enzymes catalyse reactions and follow Michaelis-Menten kinetics. The rate can be described on the basis of the concentration of the substrate and the enzymes. For a single enzyme and single substrate, the rate equation is ... 

In evaluation of kinetic parameters, the double reciprocal method is used for linearisation of the Michaelis-Menten equation (5.7.3). 

The values of the Michaelis-Menten kinetic parameters, Vj3 and C,PP characterise the kinetic expression for the micro-environment within the porous structure. Kinetic analyses of the immobilised lipase in the membrane reactor were performed because the kinetic parameters cannot be assumed to be the same values as for die native enzymes. 

The initial reaction rate (v0) obtained from each substrate concentration was fitted to Michaelis-Menten kinetics using enzyme kinetics. Pro (EKP) Software (ChemSW product,... 

The above rate equation is in agreement with that reported by Madhav and Ching [3]. Tliis rapid equilibrium treatment is a simple approach that allows the transformations of all complexes in terms of [E, [5], Kls and Kjp, which only deal with equilibrium expressions for the binding of the substrate to the enzyme. In the absence of inhibition, the enzyme kinetics are reduced to the simplest Michaelis-Menten model, as shown in Figure 5.21. The rate equation for the Michaelis-Menten model is given in ordinary textbooks and is as follows 11... 

The parameters of the Monod cell growth model are needed i.e. the maximum specific growth rate and the Michaelis-Menten constant are required for a suitable rate equation. Based on the data presented in Tables 10.1 and 10.2, obtain kinetic parameters for... 

Shimidzu etal.111 studied the catalytic activity of poly (4(5)-vinylimidazole-co-acrylic add) 60 (PVIm AA) in hydrolyses of 3-acetoxy-N-trimethylanilinium iodide 61 (ANTI) and p-nitrophenylacetate 44 (PNPA). The hydrolyses of ANTI followed the Michaelis-Menten-type kinetics, and that of PNPA followed the second-order kinetics. Substrate-binding with the copolymer was strongest at an imidazole content of 30 mol%. The authors concluded that the carboxylic acid moiety not... 

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