How is it that Arginine is labeled R and Aspartate is labeled D? Is there a source on the list, the 'magic 20' at least with their respective letter and a reason why? I assume this is something similar to Pb Lead-Plumbum? I don't remember this from the biochemistry books I've read. They where all from the 70's, would that have mattered?

 

I will be receiving my fully up to date biochemistry reference title, but not for another three weeks!

I'm not sure there's actually any reason for the choices. Some are evident, such as A for Alanine or C for Cysteine; others slightly less so, but still you can see why, such as F for Phenylalanine.

 

I'm guessing when they got to lettering Aspartate, Glutamate, Glutamine, and the others with seemingly random letters they just used those remaining.

I was afraid of that......................I'm not so good with random lettering! Note the title Ammino..............

it's possible it's related to their names in another language

What about the names of the scientists who discovered them or something? Ah probably not! They could have numbered them......................

I don't think either of those are the case, though hermanntrude's suggestion is more likely. I remember being told that a few are alphabetical, after a fashion; e.g. Asp is D; Glu, which is one carbon longer, is E. Honestly not sure though.