Enzyme-catalyzed reaction kinetics. The preceding reaction (see question #8) is

Question

Enzyme-catalyzed reaction kinetics. The preceding reaction (see question #8) is catalyzed by an enzyme called

triose phosphate isomerase (TPI). This enzyme accelerates both the forward and reverse reactions, using either

DHAP or GAP as a substrate. Both reactions follow Michaelis-Menten kinetics, with kinetic parameters listed

below.

For the forward reaction (DHAP ----> GAP): KM = 1.2 x 10-3 M kcat = 6.5 x 104 min-1

For the reverse reaction (GAP ----> DHAP): KM = 2.5 x 10-4 M kcat = 3.7 x 105 min-1

A) Assuming that TPI binds and releases its substrates rapidly (compared to the isomerization chemistry), which

substrate binds to the enzyme with higher affinity?

B) Under the following initial conditions: [TPI] = 1 x 10-6 M, [DHAP] = 2 x 10-3 M, and [GAP] = 0 M. What is

the initial reaction velocity (vo) for the forward reaction? [Show your work on additional paper.]

Explanation / Answer

A) Km relates to the binding affinity. A small Km value means high affinity. Thus, in the above case, the binding affinity for the reverse reaction is greatest.

B) Use the Michaelis–Menten equation:
v = Vmax [S] / (Km + [S]),
where vo is the initial velocity,
Vmax is the maximum reaction rate,
and Km is the concentration at which v = Vmax/2

Also cal be written as,

vo = Kcat[Eo][[S]/Km+[S]]

Feeding all the values we have,

vo = 6.5 x 10^4 x 1 x 10^-6 x (2 x 10^-3/1.2 x 10^-3 + 2 x 10^-3)

     = 0.0406 M/min Is the initial velocity for th reaction

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