You are both right, but as Maximilian Paradiz wrote in his original question, simple inversion of NA sequence will NOT lead to inversed peptide sequence. I doubt there would be any simple mechanism for that. And it would be quite useless, because inversed protein will not have "inversed properties", it would be something completely different and unrelated.

The question is, Maximilian, how long inversed peptides you want. Of course for short sequences you will find something just by chance, but the probability decreases with every additional amino acid.

Thank you for your responses, Seema, Thomas and Mathias. From what I understand, it appears that none of the known mechanisms would lead to an amino acid sequence inversion in the "clean" manner.

Thomas, I completely agree that small peptides are likely to show sequence similarity to unrelated proteins, and if were to find a similarity as such I would not be able to reach any meaningful conclusion.

I am also aware that the inverted peptide would not have "inverse properties". The peptide would most likely be non-functional, but the rare case in which it would actually produce a useful peptide (or make a different one more fit, in the case that the inverted peptide is inserted inside a different gene) it could be amplified by selection, just like other types of mutations.

Thus far I think the conclusion is that amino acid sequence inversions in the form I previously stated do not occur in nature.