Question

Study the given data and answer the questions that follow. A sample of an enzyme called lactase was isolated from the intestinal lining of a calf. Assays were undertaken to evaluate the activity of the enzyme sample. The substrate of lactase is the disaccharide lactose. Lactase breaks a lactose molecule in two, producing a glucose molecule and a galactose molecule. Two assays were carried out.

Assay 1

Lactose concentration (% w/v)	15	15	15	15	15	15
Concentration of enzyme sample(% v/v)	0	5	10	15	20	25
Reaction rate $\mu$ mole glucose $se{c}^{-1}m{L}^{-1}$	0	25	50	75	100	125

Assay 2

Lactose concentration (% w/v)	0	5	15	20	25	30
Concentration of enzyme sample(% v/v)	5	5	5	5	5	5
Reaction rate $\mu$ mole glucose $se{c}^{-1}m{L}^{-1}$	0	15	25	35	40	40

Which of the following statements can be concluded from the two assays?

• A. The reaction rate of the lactase assay is always proportional to the amount of enzyme present.
• B. The amount of lactose in an assay has no effect on the rate of the reaction.
• C. The reaction rate of the lactase assay is proportional to the amount of lactose present.
• D. The reaction rate is proportional to the amount of enzyme present at a lactose concentration of 15%w/v.

Answer 1

The correct option is D The reaction rate is proportional to the amount of enzyme present at a lactose concentration of 15%w/v.

• The reaction rate is proportional to the amount of enzyme present at a lactose concentration of $15\%$ $w/v$. A constant lactose concentration of $15\%$ $w/v$ is kept in assay 1 and we can see that the reaction rate varies proportionally to the concentration of enzyme sample where the rate is always five times that of the enzyme sample concentration.
• But in assay 2 when the lactose concentration is varied there is no proportional relationship between reaction rate and enzyme sample concentration observed.
  Therefore the correct answer is option D.