Coming back to: Oxidation pathways for methionine and tryptophan

Oxidation pathways for methionine and tryptophan Writing it up because I had to work it out twice and would rather nobody else did.

Reading back through what has been written here about Oxidation pathways for methionine, three questions come up every time and only one has ever been answered properly.

Listing all three, with what I think the state of the answer is for each, so the thread can start further along than the last one did.

The opening post is right about the mechanism and I think understates the practical bit.

Trying to state the Oxidation pathways for methionine position in a way that someone who disagrees would recognise as fair, because I do not think the version in this thread passes that test.

Distinguishing three things in the Oxidation pathways for methionine discussion that keep getting used interchangeably: the observation, the proposed mechanism, and the recommendation that gets attached to both.

Oxidation at methionine and tryptophan: adds 16 per oxygen. Usually elutes earlier. Oxidation is common in storage, especially if the solution is exposed to light or if antioxidants are not present.

One case, stated as one case.

Oxidation at methionine or tryptophan adds sixteen per oxygen and typically elutes earlier. In aged material it is the modification that grows.

If anyone can point at the primary source I would be grateful.

Confirming post #5 from a second method, which matters more than confirming it from a second person.

Storage-related degradation and synthesis-related impurity look different on a chromatogram. A growing oxidation peak over time is not a manufacturing finding.

I would rather post the uncertainty than round it away.