Enzyme-catalyzed reaction kinetics. The reaction above (sec question #2) is cata
ID: 959237 • Letter: E
Question
Enzyme-catalyzed reaction kinetics. The reaction above (sec question #2) 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 K_M = 1.2 times 10^-3 M and k_cat = 6.5 times 10^4 min^-1. Assuming that TPI binds and releases its substrates rapidly (compared to the isomerization chemistry), which substrate binds to the enzyme with higher affinity? Under the following conditions: [TPI] = 1 times 10^-6 M, [DHAP] = 2 x 10^-3 M, and [GAP] = 0 M. What is the initial reaction velocity (V_o) for the forward reaction?Explanation / Answer
A) As kcat=Turn over frequency=Vmax/[Eo] Vmax=maximum reaction rate,[Eo]=initial enzyme concentration.For same initial enzyme concentration, both substrate has same Vmax.Also they have same km=michaelis –menten constant ,so rate of rxn for both substrate is the same.
Rate=v=Vmax[S]/Km+[S]
They bind with equal affinity.
(B)initial reaction velocity for forward=vo= Vmax[So]/Km+[So] [So]=initial substrate concentration
Kcat*[Eo]=Vmax
Vmax=6.5*10^-4 min-1 *1*10^-6 M=6.5*10^-10 Mmin-1
Vo=(6.5*10^-10 Mmin-1) (2*10^-3)/(1.2*10^-3M)+( (2*10^-3)
=13*10^-13/3.2*10^-3 Mmin-1
=4.0625 *10^-10 Mmin-1(Answer)
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