--%>
Assignment Help - homework help

Explain the mechanism of Enzyme Reactions.

A mechanism for enzyme-catalyzed reactions that leads to the typical rate equation for these reactions can be described.

A variety of rate equations are required to portray the rates of enzymes catalyzed reagents and physical conditions that are encountered. The rate equation of however, is a guide to many of these variations, and the mechanisms of this section, often called the Michaelis-Menten mechanism, is likewise a base for other variations.

The mechanism that accounts for the rate equation is similar to those dealt in with.

With S representing substrate, E the enzyme, and E. S and enzyme substrate complex, the mechanism is presumed to be adequately represented by 

E + S 376_Enzyme reactions.png E. S

E. S 376_Enzyme reactions.png E + products

The steady state assumption, which, however, is not always clearly applicable in these reactions, leads to

k1[E][S] = k-1[E. S] + k2[E. S]

And [E. S] = k1/k-1 + k2 [E][S]

To bring these expressions to a form that can be compared with the empirical rate equation, we must recognize that only [Etot] = [E] + [E. S], and not [E], is generally known. Often, in fact, only a quantity proportional to [Etot], and not even values of [Etot], is available.

Replacement of [E] in equation by [E] = [Etot] - [E. S] leads to

[E. S] = k1[Etot][S]/(k-1 + k2) + k1[S]

Now this expression for the intermediate E. S can be inserted into the expression for the rate of the net reaction. This rate can be based on the formation of products in the second mechanism step. We have

-d[S]/dt = R = k2[E. S] = k1k2[Etot][S]/k-1 + k2 + k1[S]

= k2[Etot][S]/k-1 + k2)/k1 + [S]

It is customary for the term (k-1 + k2)/k1 to be obtained by the new symbol KM, that is,

KM = k-1 + k2/k1 to give the rate equation result of this mechanism as

R = k2[Etot][S]/KM + [S]

We have come at this stage to the form of the empirical rate equation obtained, we are now in a position to intercept the values of the parameters KM and k2[Etot] in terms of their roles in the roles in the steps of the mechanism.

Reference to equation shows that, as the reaction is proceeding

[E][S]/[E. S] = KM

Thus KM is related to species concentrations, as is the dissociation equilibrium constant for the species [E. S]. the value of KM, however, is given by (k...1 + k2)/k1, and this equal to the value of the dissociation constant for [E. S] only to the extent that k2 is small and can be neglected compared with k...1. Thus when the breakup of the E. S complex to form original E and S species dominates the process whereby the complex forms products, the value of KM approaches the dissociation constant for the E. S complex.

What, now, is the significance of the term k2[Etot]? One first notes that the rate of the overall reaction is

R = k2[E. S]

It follows that k2[Etot] is the rate that the reaction would have if all the enzyme were in the form of the enzyme-substrate complex. Thus k2[Etot] is the maximum rate for a given value of [Etot]. The turnover rate of an enzyme in a particular enzyme-catalyzed reaction is the rate per mole of enzyme, i.e. the turnover rate is equal to the value of k2, and this can be calculated fromk2[Etot] if the total enzyme concentration is known.

   Related Questions in Chemistry

  • Q : Molecular mass from Raoults law Provide

    Provide solution of this question. Determination of correct molecular mass from Raoult's law is applicable to: (a) An electrolyte in solution (b) A non-electrolyte in a dilute solution (c) A non-electrolyte in a concentrated solution (d) An electrolyte in a liquid so

    		•
  • Q : Linde liquefaction process Liquefied

    Liquefied natural gas (LNG) is produced using a Linde liquefaction process from pure methane gas at 3 bar and 280 K (conditions at point 1 in figure below). A three-stage compressor with interceding is used to compress the methane to 100 bar (point 2). The first stage

    		•
  • Q : Problem on Adiabatic expansion

    Calculate the change in entropy for the system for each of the following cases. Explain the sign that you obtain by a physical argument a) A gas undergoes a reversible, adiabatic expansion from an initial state at 500 K, 1 MPa, and

    		•
  • Q : Describe Transformation Matrices. Each

    Each symmetry operation can be represented by a transformation matrix.You have seen what happens when a molecule is subjected to the symmetry operation that corresponds to any of the symmetry elements of the point group to which the molecule belongs. The m

    		•
  • Q : Determining mole fraction of water in

    A mixture has 18 g water and 414 g ethanol. What is the mole fraction of water in mixture (suppose ideal behaviour of mixture): (i) 0.1  (ii) 0.4  (iii) 0.7  (iv) 0.9 Choose the right answer from abo

    		•
  • Q : Reason for medications contain hcl What

    What is the reason behind this that some medications contain hcl?

    		•
  • Q : Problem based on molality of glucose

    Select the right answer of the question. If 18 gm of glucose (C6H12O6) is present in 1000 gm of an aqueous solution of glucose, it is said to be: (a)1 molal (b)1.1 molal (c)0.5 molal (d)0.1 molal

    		•
  • Q : Einsteins mass energy relation In

    In Einstein’s mass energy relation e = mc2 for what is c employed or why is light needed for the reactions. As the reactions are with the help of neutrons?

    		•
  • Q : Calculating molarity of a solution

    Select the right answer of the question .The molarity of a 0.2 N N2Co3 solution will be: (a) 0.05 M (b) 0.2 M (c) 0.1 M (d)0.4 M

    		•
  • Q : Mole fraction of water Give me answer

    Give me answer of this question. A solution contains 25%H2O 25%C2H5OH , and 50% CH3 COOH by mass. The mole fraction of H2O would be: (a) 0.25 (b) 2.5 (c) 0.503 (d) 5.03.

    		•