Becker's World of the Cell 9th Edition by Lewis Kleinsmith, Jeff Hardin, Gregory Paul Bertoni

Exercise 6

Enzyme Kinetics. The enzyme -galactosidase catalyzes the hydrolysis of the disaccharide lactose into its component monosaccharides:
(1)
To determine V max and K m of -galactosidase for lactose, the same amount of enzyme (1 µ g per tube)was incubated with a series of lactose concentrations under conditions where product concentrations remained negligible. At each lactose concentration, the initial reaction velocity was determined by assaying for the amount of lactose remaining at the end of the assay. The following data were obtained:

(a)Why is it necessary to specify that product concentrations remained negligible during the course of the reaction
(b)Plot v (rate of lactose consumption)versus [S] (lactose concentration). Why is it that when the lactose concentration is doubled, the increase in velocity is always less than twofold
(c)Calculate 1/v and 1/[S] for each entry on the data table, and plot 1/v versus 1/[S].
(d)Determine K m and V max from your double-reciprocal plot.
(e)On the same graph as part b, plot the results you would expect if each tube contained only 0.5 / µ g of enzyme. Explain your graph.