Enzyme Modifications

Question 1

Phosphorylation

Answer 1

• Covalent modification
• Kinases add a phosphate group to Serine, Threonine or Tyrosine hydroxyl groups (STT)
• Changes in phosphorylation are initiated by some external signal, ex. a hormone or neurotransmitter
• Alters the activity of the enzyme
  1. Introduces negative charge
  2. Disrupts or forms electrostatic interactions
  3. Can form hydrogen bonds
• Reversible through the actions of phosphatase
• Activity may be increased or decreased, effect is specific to the enzyme

Question 2

Acetylation

Answer 2

• Covalent modification

- Addition of an acetyl group on the amino terminus of Lysine

Question 3

ADP-ribosylation

Answer 3

• Covalent modification

- Introduces a bulky structure to the nitrogen group on Arginine or Glutamine, or the sulfur group on Cysteine

Question 4

Zymogen Activation

Answer 4

Irreversible conversion of an inactive precursor to active enzyme by cleavage of covalent bonds

Ex. Trypsinogen and Chymtrypsinogen

Question 5

Palmitoylation

Answer 5

• Lipid addition to the internal SH group of Cysteine

- Modification that determines intercellular location and activity

Question 6

Myristoylation

Answer 6

• Lipid addition to the NH group of the N - terminus of Glycine
• Modification that determines intercellular location and activity

Question 7

Prenylation

Answer 7

• Lipid addition to the SH group of Cysteine

- Modification that determines intercellular location and activity

Question 8

O-glycosylation

Answer 8

• Carbohydrate addition to the OH group Serine, Threonine or Tyrosine
• Can determine intracellular/extracellular location

Question 9

N-glycoslyation

Answer 9

• Carbohydrate addition to the NH2 group of Asparagine

- Can determine intracellular/extracellular location