Lecture_18-Michaelis-Menten_Equation_copy

# Lecture_18-Michaelis-Menten_Equation_copy - the number of...

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ENZYME KINETICS The Michaelis-Menten Equation The date of Exam 3 has been changed: New Date: November 9, 2011 rate [S] V max y = x x + C y = V max x x + C v 0 = k 2 E [ ] total S [ ] S [ ]+ k 1 + k 2 ( ) k 1 = V max S [ ] S [ ]+ K M E + S E•S E + P k 1 k 2 k- 1 The Michaelis-Menten Parameters V max K M : maximal velocity of the enzyme : [S] where v 0 = ½ V max v 0 = V max S [ ] S [ ] + K M ± K M approximates the afFnity of the enzyme for the substrate

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E [ ] free S [ ] total E S [ ] = k 1 + k 2 ( ) k 1 = K M E + S E•S K D K D = E [ ] free S [ ] total E S [ ] K M includes a k 2 rate constant and is therefore not a true dissociation constant (unless k 2 << k -1 ) E + S E•S E + P k 1 k 2 k- 1 The Michaelis-Menten Parameters V max K M k cat k cat K M : maximal velocity of the enzyme : [S] where v 0 = ½ V max : turnover number : speciFcity constant v 0 = V max S [ ] S [ ] + K M v 0 = V max S [ ] S [ ]+ K M = k 2 E [ ] total S [ ] total S [ ] total + K M V max = k 2 E [ ] total V max E [ ] total = k 2 = k cat v 0 = k cat E [ ] total S [ ] total S [ ] total + K M v 0 = k cat E [ ] total S [ ] total S [ ] total + K M What happens to the equation if [S] total >> K M ? v 0 = k cat E [ ] total S [ ] total S [ ] total = k cat E [ ] total At really high [S], the rate is dependent only on [E] total . k cat is a Frst-order rate constant
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Unformatted text preview: the number of substrate molecules that are converted to product by one active site when [S] is high relative to K M . called the turnover number v = k cat E [ ] total S [ ] total S [ ] total + K M What happens to the equation if [S] total << K M ? v = k cat E [ ] total S [ ] total K M = k cat K M E [ ] total S [ ] total At really low [S], the rate is dependent on [E] total and [S] total k cat /K M is a second-order rate constant describes the enzymes efFciency . called the speciFcity constant . k cat (s-1 ) K M (mM) k cat /K M (M-1 s-1 ) Sub. 1 1,000 10 1 x 10 5 Sub. 2 10 0.001 1 x10 7 Example: A hydrolases activity is measured with two different substrates. The k cat and K M results are below. Which substrate is the better one for the enzyme?...
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## This note was uploaded on 11/28/2011 for the course CHEM 340 taught by Professor T.baird during the Fall '11 term at S.F. State.

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Lecture_18-Michaelis-Menten_Equation_copy - the number of...

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