The protein catalase catalyzes the reaction described by The protein catalase ca

Question

The protein catalase catalyzes the reaction described by

The protein catalase catalyzes the reaction described by 2H_2O_2(aq) rightarrow 2H_2 O(l) + O_2(g) and has a Michaelis-Menten constant of K_m = 25 mM and a turnover number of 4.0 times 10^7 s^-1. The total enzyme concentration is 0.029 mu M and the initial substrate concentration is 5.05 mu M. Catalase has a single active site. Calculate the value of R_max (often written as V_max) for this enzyme. Calculate the initial rate, R (often written as V_0), of this reaction.

Explanation / Answer

1) Turnover number Kcat = Vmax/ [E]

Vmax = Kcat. [E]

= 4 x 107 s-1 x 0.029 x 10-6 M

= 1.16 M s-1

= 1160 x 10-3 Ms-1

= 1160 mM.s-1

  Vmax = 1160 mM.s-1

Hence, Rmax = 1160 mM.s-1

2) Vo = (Vmax[S]) /Km + [S]

Here, Km >> [S] , hence

Vo = (Vmax[S]) /Km

= 1.16 M s-1 x 5.05 x 10-6 M / [ 0.015 M]

= 390.5 x 10-6 M s-1

   = 0.39 mM.s-1

  Vo = 0.39 mM.s-1

Therefore,

R = 0.39 mM.s-1

  

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