Kinetics ping-pong

If the enzyme-catalyzed reaction is to be faster than the uncatalyzed case, the acceptor group on the enzyme must be a better attacking group than Y and a better leaving group than X. Note that most enzymes that carry out covalent catalysis have ping-pong kinetic mechanisms. 

FIGURE 19.34 The galactose-l-phosphate uridylyltransferase reaction involves a ping-pong kinetic mechanism. 

Acetyl-CoA Carboxylase Is Biotin-Dependent and Displays Ping-Pong Kinetics... 

In nature, aminotransferases participate in a number of metabolic pathways [4[. They catalyze the transfer of an amino group originating from an amino acid donor to a 2-ketoacid acceptor by a simple mechanism. First, an amino group from the donor is transferred to the cofactor pyridoxal phosphate with formation of a 2-keto add and an enzyme-bound pyridoxamine phosphate intermediate. Second, this intermediate transfers the amino group to the 2-keto add acceptor. The readion is reversible, shows ping-pong kinetics, and has been used industrially in the production ofamino acids [69]. It can be driven in one direction by the appropriate choice of conditions (e.g. substrate concentration). Some of the aminotransferases accept simple amines instead of amino acids as amine donors, and highly enantioselective cases have been reported [70]. 

The two substrate kinetics of the overall reaction catalyzed by the complex in permeabilized membranes showed classical ping-pong kinetics in accordance with a phosphorylated enzyme intermediate. The affinity constants for fructose and P-enolpyruvate were 8 and 25 /iM, respectively. 

Toluene, hexane, diisopropylether, trichloroethane Evaluation of the ping-pong kinetics [135]... 

Although Equation 4, Equation 5, Equation 6, and Equation 7 may be used to establish the E-value of a catalyst in many cases of interest, they certainly do not cover the full range of possible situations. This holds in particular for the commonly employed hydrolases that show bi bi ping pong kinetics. For enzymes that follow this kinetic scheme, the ratio of reaction rates in the case of a so-called A-P resolution, Ars + <=> PR-S + Q (see [31]) takes the following form (Equation 7) ... 

Figure 2.4 Schematic profile for the acylation stage involving the R-enantiomer of an enantioselective reaction catalyzed by an enzyme that follows bi bi ping pong kinetics. The reaction is an example of the so-called A-...

Product inhibition (Section A,12) can also provide information about mechanisms. For example, if 1 / v is plotted against 1 / [A] in the presence and absence of the product Q, the product will be found to compete with A and to give a typical family of lines for competitive inhibition. On the other hand, a plot of 1 / v vs 1 / [B] in the presence and absence of Q will indicate noncompetitive inhibition if the binding of substrates is ordered (Eq. 9-43). In other words, only the A-Q pair of substrates are competitive. Product inhibition is also observed with enzymes having ping-pong kinetics (Eq. 9-47) as a result of formation of nonproductive complexes. 

Fiqure 3.6 The characteristic parallel-line reciprocal plots of ping-pong kinetics. As the concentration of the second substrate in the sequence increases, Vmlx increases, as does the Ku for the first substrate. VmaJKM, the reciprocal of the slope of the plot, remains constant (see equation 3.68). 

In many ways, ping-pong kinetics is the most mechanistically informative of all the types of steady state kinetics, since information is given about the occurrence of a covalent intermediate. The finding of ping-pong kinetics is often used... 

B that is the double reciprocal plots for a ping-pong kinetic mechanism are parallel lines—the slopes are not changed by altering the concentration of the second substrate. 

The above poem [89] reflects the notion that transporters operating according to the Singer model should exhibit ping-pong kinetics. Ping-pong kinetics are observed in... 

Careful analysis of the effect of the concentrations of the counter ions on transport parameters and have not been performed as a test for ping pong kinetics. However, one can compare and of net uptake with the exchange... 

Figure 4-46 A sdiematic representation of a Ping Pong kinetic mechanism for a group transfer reaction. The donor A reacts with E to form a substituted enzyme P leaves before the acceptor, B, adds.

Levansucrase is a transfructosylase which converts sucrose to levan , a largely p(2 6)-linked fructofuranose polymer, and has been investigated because of its synthesis by oral bacteria. The levans and dextrans produced from dietary sucrose are sparingly water soluble and contribute to the build-up of dental plaque on the teeth. The enzyme from Bacillus subtilis was shown to have ping-pong kinetics,and the intermediacy of a covalent, fructosylated... 

The double-displacement mechanism with its covalent intermediate can often be distinguished from single displacement reactions by kinetic experiments in which an appropriate nudeophilic spedes is added to reaction solutions of enzyme and substrate and allowed to compete with water for the covalent intermediate. The dependence of initial velocity on the concentrations of substrate and added nucleophile will produce a distinctive kinetic pattern (i.e., ping-pong kinetics). Observation of such a pattern constitutes strong evidence suggesting that the hydrolase under study effects catalysis through a double-displacement mechanism. 

Despite the facts cited above, which are undisputed, the mechanism of reaction (16) is no longer believed to involve a double displacement or a phosphoenzyme. The apparent Ping-Pong kinetics, the rates of the exchange reactions (16a) and (16b), and the isolated phosphoenzyme fail to meet the most rigorous criteria for the double-displacement mechanism. And the exchange re-... 

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