Protein Oxidation

Question 1

Which compounds react faster with OH than antioxidants/

Answer 1

Collagen = 4 x10 (11)  dm3 mol-1 s-1 
Albumin = 8 x 10(10) dm3 mol-1 s-1
Ascorbate = 1 x 10(10)
GSH = 1.4 x 10(10)

Question 2

What are the primary mechanisms of oxidative damage to proteins.

Answer 2

AA residue side chains 
- H abstraction (aliphatic) 
- H addition (aromatic)
Protein backbone 
- H abstraction at a-C --> backbone fragmentation

Question 3

What are the features of protein carbonyls that aid research use?

Answer 3

Stable 
Low levels in most proteins 
2 to 8 fold elevation during OS in vivo 
Induced in vitro by most oxidants
Sensitive assays

Question 4

When / how do cysteine groups become thiolated (and therefore redox active)?

Answer 4

Free cysteines have pKa of 8.5 at neutral pH.

Need pKa below 7.4 - achieved by H-bonding or adjacent basic AA residues.

Question 5

What are the characteristic reactions of aromatic side chains?

Answer 5

Addition (form diverse set of products depending on added species)
Electron abstraction less common and yields hydroxylated products.
Similar products in presence and absence of O2.

Question 6

Why are electron rich side chains the most reactive. Give examples.

Answer 6

Trp, Tyr, His, Met.

Most radicals are electron deficient.

Question 7

What is the effect of S-nitrosylation on proteins?

Answer 7

Induced by NO, ONOO- on Cys residues.

Penna et al showed favourably produced during cardiac preconditioning.