Please explain the following clearly. A certain enzyme with alpha_4 quaternary s

Question

Please explain the following clearly.

A certain enzyme with alpha_4 quaternary structure contains one active site per 85 kDa subunit. A series of enzyme assays with (and without) an inhibitor are carried out. Each enzyme assay contained 3.3 mu g of enzyme. The enzyme assay data is plotted below. Answer the questions that follow. Clearly show all of your work. DEFINE k_cat then use the data above to CALCULATE the value of k_cat (min^-1) in the absence of inhibitor. DEFINE K_m AND then calculate its value (in mM) using the data above.

Explanation / Answer

(a) From the plot

intercept at y-axis = 1/Vmax = 2.5

Vmax = 1/2.5 = 0.4 umol/L.min

Kcat = Vmax/[Et]

[Et] = 3.3 ug/85000 = 4 x 10^-5 umol

So,

Kcat = 0.4/4 x 10^-5 = 10,000 min-1

(b) Km = -1/intercept on x-axis

            = -(-1/1 mM)

            = 1 mM

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