Protein Oxidation

# Tyrosine oxidation: When there are 2 tyrosine molecules together, the 2 radicals can also form a crosslink D-tyrosine, it is a natural process happening during the aging of meat. When the animal is getting older there is more production of D-tyrosine, and as result of it the muscles become tougher. It is an example of a protein oxidation reaction.

# Methionine can be oxidized into a sulfoxide and get homocysteine. Sulfoxide in the body can be back reduced into methionine (cost a lot of energy). At the moment you get the sulfone then it is not nutritionally relevant. Metionine is essencial.

# Cysteine is the most vulnerable amino acid towards oxidation, because of the free sufridril group. The free sulfridril group can be further oxidized by another sulfridril group, so can get a dimer (disulfride brigde, cysteine). It can be stepwise oxidized into the mono or disulfoxide and sulfone. Until disulfoxide it can g back, but when it gets to sulfone, there is no way back.

The formation of cysteine (disulfide bridge) is important during bread making. The Polymerization reactions of wheat protein (glutelins and gliamines, which are prolamines) produce a protein network, which is largely base on the production of the disulfite bridges. This chemistry (dimerization of cysteine) is important to improve the dough structure, and build up the gluten network during bread making.   So oxidants are used as bread improvers such a bromates (now prohibited due toxicity, were used in UK)

# Tryptophan is the 2^nd most important amino acid with regards to oxidation. It is rather unstable. After a some of steps, it can produce Formilkiruninie and qinurinine which is toxic.