Enzyme Kinetics and Proteins

Question 1

Define pK.

Answer 1

pK is a measure of the strength of an acid. It indicates whether an amino acid is polar, no polar or charged.

Question 2

Define pI.

Answer 2

Isoelectric point of a protein, the pH at which there is no net charge.

Question 3

Define Km.

Answer 3

Michaelis constant, a measure of the affinity of an enzyme for a substrate.
Low Km means high affinity. High Km means low affinity.

Question 4

Define V0.

Answer 4

Rate of an enzyme catalysts rxn at time 0, when all substrate is available to form product.

Question 5

Define Vmax.

Answer 5

The max rate that the enzyme can catalyze the rxn at if all the active sites were saturated.

Question 6

What is a unit of enzyme activity?

Answer 6

It is the amount of substrate that the enzyme can convert into product in a given time under standard conditions.
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Question 7

Hexokinase vs glucokinase.

Answer 7

Hexokinase has a lower Km value and thus a higher affinity for glucose —> glucose-6-P. This means that it will catalyze the rxn even at very low conc a of glucose.
Glucokinase is involved in the same rxn to store glucose as glycogen in the liver. It has a higher Km value and so lower affinity for glucose. This means that it will only be activated when blood glucose is higher than 5 mM to start storing glucose as glycogen.
Hexokinase approaches Vmax faster than glucokinase.