a) What type of inhibition is mediated by [I], as determined by evaluation of a

Question

a) What type of inhibition is mediated by [I], as determined by evaluation of a double-reciprocal plot (Lineweaver-Burke)? How do you know?

b) Conceptually, how is the inhibitor interacting and preventing catalysis? (Does it compete with substrate, deplete functional enzyme, other ways...?) How does it effect the KM and Vmax?

c) What is the Ki (or Ki’) for this [I]? What type of plot do you use to find this?

Explanation / Answer

Lineweaver-Burke plot is 1/V= (KM/Vmax)1/S +1/Vmax

the plots for all the three cases given is shown below

for the case of no inhibition, intercept, 1/Vmax= 0.303min/mM, Vmax= 1/0.103 = 9.71 mM/min

KM/Vmax = 0.247, KM= 0.247*9.71 =2.4 mM

since KM/Vmax the slope remained constant, this is uncompetitive inhibiton. This is as a result of Inhibitor binding to Enzyme substrate complex.

1/V= (Km/Vmax)*1/S + alpha/Vmax, where alpha = (1+I/KI)

for inhibition

I=0.5, alpha/Vmax= 0.203, alpha =0.203*9.71= 1.97, 1+I/KI= 1.97, I/Ki=0.97, Ki = I/0.97= 0.5/0.97= 0.515 mM

I=1, alpha/Vmax= 0.303, alpha= 0.303*9.71= 2.94, I/Ki= 1.94, Ki= 1/1.94=0.515mM

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