Lecture 2 August 3, 2005 Lehninger (4 th Edition), Chapter 6,

ENZYME KINETICS LNC Chapter 6

REACTANTS SUBSTRATES PRODUCTS k First order reactions:A  P k Second order reactions:A + B  P A + A  P

1 st order:ln[A] = ln[A o ] - kt or [A] = [A o ] exp(-kt) 2 nd order: 1/[A] = 1/[Ao] + kt

TRANSITION STATE THEORY A C B D A C B D A C B D A catalyst serves in at least two ways: it binds and aligns the substrates it facilitates the redistribution of electrons (charges)

k 1 k 2 E + S ES Products k -1 CHAPTER 6 Enzymes and Enzyme Kinetics

Fig. 6-2

Fig. 6-3

Derivation of Michaelis-Menten equation 1. equilibrium assumption: k -1 >> k 2 2. steady state assumption:d[ES]/dt = 0 Note:[E] = [E] total – [ES]

Hmmm..??

when [S] >> K m then v  v max and v max = k 2 [E] T k 2 x [E] T x [S] v = K m + [S]

k -1 + k 2 K m = k 1

d K m K d when k -1 >> k 2

Fig. 6-11

Fig. 6-12

1 K m 1 1 = x + v o v max [S] v max y = ax + b

Lineweaver-Burk Plot Double Reciprocal Plot box. 6-1

- another definition : v max k 2 = k cat = [E] T TURNOVER NUMBER

molecules of substrate / molecule of enzyme / second moles of substrate / mole of enzyme / second

Reactions with more than one substrate (more typical) Overall reaction: S 1 + S 2 P 1 + P 2

Fig. 6-13

LNC 6-14 a Lines intersect: ternary complex is formed in the reaction

LNC 6-13 b This case is also referred to as the Ping-Pong or double displacement mechanism

LNC 6-14 b Lines do not intersect: no ternary complex is formed

Enzyme Inhibitors

Fig. 6-15a

Competitive Inhibition  = 1 + [I] / K I box

Fig. 6-15b

Uncompetitive Inhibition  ’ = 1 + [I] / K I box

Fig. 6-15c

Mixed Inhibition When  =  ’, then we also speak of noncompetitive inhibition box 6-2.3

LNC 6-28 FEEDBACK INHIBITION

LNC 6-26

LNC 6-27 ASPARTATE TRANSCARBAMYLASE

LNC 6-29a

LNC 6-29b

LNC 6-29c

Part III Bioenergetics and Metabolism Chapter 13 in LNC

THE CARBON CYCLE

urea THE NITROGEN CYCLE

Types of Organic Reactions 1) Group transfer Glucose + ATP Glu-6-P + ADP H 2 O + ATP P i + ADP 2) Oxidation-reduction reactions Ethanol + NAH + acetaldehyde + NADH + H + 3) Eliminations, isomerizations, rearrangements aldose ketose 4) reactions involving making or breaking of C-C bonds Fru-1,6, bisphosphate dihydroxyacetone-phosphate + glyceraldehyde-3phosphate

End of Lecture 2 Aug. 3, 2005