Question

Consider the enzyme-catalyzed reaction A → B. You determine experimentally that the maximal initial velocity, Vmax, for the amount of enzyme you have added is 100 units. You also determine that the Michaelis constant, Km, for this enzyme is 80 μM. What concentration of A will give an initial velocity of 60 units? (Note that the units for velocity can be ignored here; they will be relevant in another question. HINT: you need do NO calculations.) The answer is 120, what is the explanation?

Answer 1

• Enzymes are molecules usually protein that help in catalyzing biochemical reactions, by binding substrates to their active or catalytic site.
• The activity of an enzyme may be induced or inhibited, accelerated or retarded by several factors.
• Some of such factors are temperature, pH, concentration of enzyme and substrate, presence of activators or inhibitors, etc.

• Rate of enzyme activity may be related using Michalis-Menten equations.

• Michaelis-Menten equation may be derived as:

  V0 = Vmax [S]/ KM+[S]

  · Vmax = At maximum substrate concentration or saturation, the maximum velocity obtained.

  · KM = Michaelis constant: It is described as the concentration of substrate concentration when the velocity is half or 50% of maximum velocity. OR, Vmax/2

  · [S] = concentration of the substrate.

Given:

Vmax = 100 units

KM = 80 µm

V0 = 60 units

100 S = 60 (80 +S)

100 S= 4800 + 60 S

40S = 4800

OR

S = 4800/40 = 120 µm