Enzyme Catalysis (26.4) Enzymes are catalysts, so their kinetics can be explained in the same fashion Enzymes – Rate law for enzyme catalysis is referred to as the Michaelis-Menten rate law – K m is called the Michaelis constant When the substrate concentration is very large, the rate depends only on the concentration of enzyme and the turnover rate (k 2 ) – Equilibrium between reactants and enzyme-substrate complex (ES) is pushed to the right (i.e., only ES exists, no free enzyme) – When [S] >> K m, the maximum rate is achieved (R max ) One can get K m by realizing that it is equal to [S] when the rate is half of the maximum rate – If K m is small, then the enzyme tightly binds the substrate (equilibrium is shifted to ES)

R max and K m (26.4) Constants from Michaelis-Menten equation give insight into qualitative and quantitative aspects of enzyme kinetics Constants – Indicate if enzyme inhibition is present and what type of inhibition is exhibited – R max is the maximum possible rate of conversion of substrate to product for a given enzyme – K m is related to how tightly an enzyme binds a substrate (the higher the value, the less tightly bound the substrate) Inverting the Michaelis-Menten rate law gives an equation that can be useful for obtaining the maximum rate and the Michaelis constant – Lineweaver-Burk plot is generated by plotting 1/rate vs. 1/[S] Lineweaver-Burk plot Lineweaver-Burk equation is more useful for getting constants since experiments can be done over a short range of substrate concentrations – y-intercept gives us R max, which is then used with the slope to get K m

Enzymes as Catalysts

Michaelis-Menten Plot for Catalyzed Reaction of CO 2 with H 2 O

Lineweaver-Burk Plot for Catalyzed Reaction of CO 2 with H 2 O