1. In the presence of a non-competitive inhibitor a Lineweaver-Burk plot has a h
ID: 195556 • Letter: 1
Question
1. In the presence of a non-competitive inhibitor a Lineweaver-Burk plot has a higher y-intercept than a control (without any inhibitor), and the x intercept is the same as that for the control. Explain what this indicates 2. In the presence of a competitive inhibitor a Lineweaver-Burk plot has the same y-intercept as a control 3. Why is specific activity used as a measurement of enzyme purity, but the turnover number cannot be 4. Why is a V vs S plot often inadequate for determining enzyme kinetic constants, and how do various (without an inhibitor), but has a higher (less negative) x-intercept. Explain what this indicates. used for this purpose? alternate plotting methods allow these values to be determined more adequately? Give examples of alternate methods of kinetic analysis and their utility.Explanation / Answer
1. In non-competitive inhibition, the inhibitor binds to a site other than the active site of the enzyme. As it does not bind in the enzyme’s active site, it does not directly compete for the active site with the substrate. The binding to the secondary site changes the conformation of the enzyme so that the active site can no longer bind the substrate. The Michaelis-Menton constant Km will not change as binding affinity to active site is not changed. Km is the substrate concentration at half the maximum velocity. The Lineweaver berg plot is a plot of 1/V vs 1/[S]. The X intercept is -1/Km. Hence, if Km does not change, the x-intercept will also not change. The y-intercept is the 1/Vmax. Vmax is the maximum velocity of the reaction. Few active sites are available as due to change in conformation. Hence, the reaction velocity and consequently Vmax will decrease in non-competitive inhibition. Hence , 1/Vmax will increase, giving a higher y-intercept.
2. in competitive inhibition, the inhibitor competes with the substrate for the active site of the enzyme, due to structural similarities. The enzyme preferentially binds the inhibitor as the inhibitors are designed to have higher affinity for the enzyme. Hence, apparent Km will increase as the substrate has less affinity. Hence, x-intercept (-1/Km) will have a smaller absolute value and will shift to the right. It therefore has a higher or less negative value. The Vmax, however remains the same as the rate of reaction is not affected. Hence, y-intercept remains unaltered.
3. Specific enzyme activity is the activity of an enzyme per milligram of total protein (expressed in mol min1mg1). It is the moles of product formed in a specific time per mg of protein. Purity is the specific activity of enzyme sample / specific activity of pure enzyme. Hence, specific activity determines the purity of the enzyme. A lower specific activity will indicate an impure enzyme.
Turnover number, is the number of substrate molecules metabolized per enzyme molecule per unit time. Its units are min-1 or s -1. Molecular activity of the enzyme is the activity of the enzyme depending on the molecular weight. Molecular activity determines the turnover number. As it has no link to purity, it cannot be used to determine whether an enzyme is pure or not. It is a characteristic specific of a particular enzyme only.
As per Chegg’s rule, only one question needs to be answered.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.