Initial rate data for an enzyme that obeys Michaelis-Menten kinetics are shown i

Question

Initial rate data for an enzyme that obeys Michaelis-Menten kinetics are shown in the following table. When the enzyme concentration is 3 nmol ml?1, a Lineweaver-Burk plot of this data gives a line with a y-intercept of 0.00426 (?mol?1 ml s).

Part A: Calculate Kcat for the reaction. Correct Answer: 7.82*10^4 s^-1

Part B: Calculate Km for the enzyme.

Part C: When the reactions in part (B) are repeated in the presence of 12 ?M of an uncompetitive inhibitor, the y-intercept of the Lineweaver-Burk plot is 0.352 (?mol?1 ml s). Calculate K?I for this inhibitor.

Please help with Part B and C if you can. I have been really struggling with the correct way to accomplish this. I made my inverse data table but am having problems knowing how to set up my linear equation to come up with the correct Km.

[S] ?M v0 (?mol ml?1 s?1) 320 169 160 132 80.0 92.0 40.0 57.2 20.0 32.6 10.0 17.5

Explanation / Answer

Part B

Equation of line is y = 0.5287x + 0.0043

Slope = 0.5287, intercept = 0.0043

VMax = 1 / intercept = 1 / 0.0043 = 232.6     (for intercept = 0.00426, VMax = 234.7)

Slope = KM / VMax

KM = Slope x VMax = 0.5287 x 232.56 = 123   (for intercept = 0.00426, KM = 1240.1)

Part C

Now intercept = 0.352

Intercept also = ( 1 + [I] / KI ) / VMax )

Intercept x VMax = 1 + [I] / KI

0.352 x 232.6 = 1 + [12] / KI

81.9 = 1 + [12] / KI

80.9 = [12] / KI

KI = 12 / 80.9

KI = 0.1484 ( for VMax = 234.7, KI = 0.1470)

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