Constant Michaelis

Michaelis constant An experimentally determined parameter inversely indicative of the affinity of an enzyme for its substrate. For a constant enzyme concentration, the Michaelis constant is that substrate concentration at which the rate of reaction is half its maximum rate. In general, the Michaelis constant is equivalent to the dissociation constant of the enzyme-substrate complex. 

Km for an enzymatic reaction are of significant interest in the study of cellular chemistry. From equation 13.19 we see that Vmax provides a means for determining the rate constant 2- For enzymes that follow the mechanism shown in reaction 13.15, 2 is equivalent to the enzyme s turnover number, kcat- The turnover number is the maximum number of substrate molecules converted to product by a single active site on the enzyme, per unit time. Thus, the turnover number provides a direct indication of the catalytic efficiency of an enzyme s active site. The Michaelis constant, Km, is significant because it provides an estimate of the substrate s intracellular concentration. 

Figure 11.1 A plot of the reaction rate as a function of the substrate concentration for an enzyme catalyzed reaction. Vmax is the maximal velocity. The Michaelis constant. Km, is the substrate concentration at half Vmax- The rate v is related to the substrate concentration, [S], by the Michaelis-Menten equation ...

Equation 1-108 can be considered as the Michaelis-Menten equation, where is the Michaelis constant and represented as... 

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... 

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]. 

Equation (3-150) is the Michaelis-Menten equation, Vm is the maximum velocity (for the enzyme concentration ,), and is the Michaelis constant. 

The Michaelis constant has the units of a dissociation constant however, the dissociation constant of the enzyme—substrate complex is k dk, which is not equal to Km unless k 2-... 

Properties of the luciferases. According to Shimomura and Flood (1998) and Shimomura et al. (2001), all Periphylla luciferases L, A, B and C catalyze the oxidation of coelenterazine, resulting in the emission of blue light (Amax 465 nm). Luciferases B (40 kDa) and C (80 kDa) are apparently the dimer and tetramer, respectively, of luciferase A (20 kDa). The presence of a salt is essential for the activity of luciferase, and the optimum salt concentration is about 1M in the case of NaCl for all forms of luciferases. The luminescence intensity of luciferase L is maximum near 0°C, and decreases almost linearly with rising temperature, falling to zero intensity at 60°C the luminescence intensity profiles of luciferases A, B and C show their peaks at about 30°C (Fig. 4.5.3). The Michaelis constants estimated for luciferases A, B and C with coelenterazine are all about 0.2 xM, and that for luciferase L is 1.2 jiM. 

Dissociation constant Michaelis constant Luciferin binding protein Lauroylcholine chloride Light unit... 

Comparison of the ordinary Michaelis-Menten relation with (5.108) shows that the inhibitor did not influence specific growth rate, vmgx, but the Michaelis-Menten constant was affected by the inhibitor and resulted in a constant, known as the apparent Michaelis constant. 

Kfvv Appai-ent Michaelis constant, g-l1 umS Apparent maximum specific growth rate constant, li 1... 

Log-concave kinetics can be due to saturable Michaelis-Menten elimination depending on the maximal metabolism capacity (Umax) and the Michaelis constant (Km). 

This form is worthwhile to note, in that many catalytic processes utilize dual substrates. The equation contains an apparent Michaelis constant, given by... 

The Michaelis constant (fCM) is an index of the stability of an enzyme-substrate complex. Does a high Michaelis constant indicate a stable or an unstable enzyme-substrate complex Explain your reasoning. 

Michaelis constant (KM) A constant in the rate law for the Michaelis—Menten mechanism. 

Michaelis constant) which determines the deviation from proportionality a small D (compared to M) corresponds to a weak dependence of S on M and a large D corresponds to a near proportional dependence. 

If, as it is usually done, the interaction of enzyme with glycal is studied in the presence of substrate S having Michaelis constant K , the observed rate constant k pp, for the approach to the steady-state inhibition has to be corrected for the competition of substrate for the free enzyme, in order to calculate the rate constants kp , kp, and k yj, from the experimental data. 

Michaelis constant K for D-glyca] hydration. Approximate value calculated from specific activity with M, 50,000. 

The Michaelis constant is the substrate concentration at which is half the maximal velocity (V 3 /2) attainable at a particular concentration of enzyme. thus has the dimensions of substrate concentration. The dependence of initial reaction velocity on [S] and may be illustrated by evaluating the Michaelis-Menten equation under three conditions. 

Stated another way, the smaller the tendency of the enzyme and its substrate to dissociate, the greater the affinity of the enzyme for its substrate. While the Michaelis constant often approximates the dissociation constant fCj, this is by no means always the case. For a typical enzyme-catalyzed reaction,... 

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