Question

1) For the following data, determine the Vmax in mM/min.

The enzyme prostaglandin synthase uses aracadonic acid as the substrate and produces product PGG2.

[S](mM)      PGG2(mM/min)

0.5               23.5

1.0               32.2

1.5               36.9

2.5               41.8

3.5               44.0

2) The enzyme prostaglandin synthase uses aracadonic acid as the substrate and produces product PGG2. If 10mM Ibuprofen inhibits this enzyme as is seen in the 3rd column.

[S](mM)      PGG2(Vo mM/min)      I (Vo mM/min)

0.5               23.5                              16.67

1.0               32.2                              25.25

1.5               36.9                              30.49

2.5               41.8                              37.04

3.5               44.0                              38.91

What is the Ki' ?

Answer 1

For the enzyme prostaglandin synthase using aracadonic acid as the substrate producing PGG2 product

1] Plot reciprocal plot

1/[S] on x-axis and 1/vo on y-axis

from the plot

Vmax = 1/0.0433 = 23.1 mM/min

2] with 10 mM Ibuprofen inhibitor

Plot reciprocal plot

1/[S] on x-axis and 1/vo on y-axis

from the plot

Vmax, apparent = 1/0.0615 = 16.3 mM/min

So,

for Ki using equation,

Vmax,apparent = Vm/(1 + [I]/Ki)

feeding values from above,

16.3 = 23.1/(1 + 10/Ki)

Ki = 24 mM

----

Data points for plot,

1/[S]	1/vo	w[I](1/vo)
2	0.0425	0.06
1	0.031	0.04
0.667	0.027	0.033
0.4	0.024	0.027
0.286	0.023	0.026

Plot