In a "yet-to-be-published" article (not on archiv, dang it), they find that the ratio of left to right handed amino acids isn't the same as on Earth either for the Tagish Lake meteorite. In fact the ratios for aspartic acid were 4:1 left:right, but were only 52:48 for alanine, compared to 1:O(0) for Earthly proteins and enzymes. Random synthesis should result in 1:1. Right-handed amino acids just don't fit in proteins. You can imagine proteins made of nothing but right-handed amino acids, but they just don't exist. Here. Though right-handed acids do rarely show up.
The carbon 13 enrichment, combined with the large left-hand excess in aspartic acid but not in alanine, provides very strong evidence that some left-handed proteinogenic amino acids — ones used by life to make proteins — can be produced in excess in asteroids, according to the team.
They point out that some amino acid crystals will be of one handedness only, and that's one way of getting a pure sample. That's nice, but amino acids aren't usually found in crystal form. I suppose one model might be that there is a pool of mixed amino acids, and a crystal of right-handed cytosine forms, leaving the left-handed in the pool to react and get turned into the first proto-proteins. Or something. Alternatively, an crystal of left-handed survives some chemical insult better than the loose pool of right-handed, and is still around to form proto-proteins. Eh.
This process only amplifies a small excess that already exists. Perhaps a tiny initial left-hand excess was created by conditions in the solar nebula. For example, polarized ultraviolet light or other types of radiation from nearby stars might favor the creation of left-handed amino acids or the destruction of right-handed ones, according to the team. This initial left-hand excess could then get amplified in asteroids by processes like crystallization.
Um. Let's suppose we have something like 100% left-handed in a sample that splashes away from Earth. Over time despite the small rate we can get C13 from p+C12->N13->C13+γ, with the solar wind or low energy cosmic rays as a source for the protons. There should be C14 as well, though I'm not sure of the ratio, and some of the transmutations might disrupt the molecule. So chemicals of terrestrial origin can start to look cosmic. If they were in solution I'd expect nuclear recoil to break the molecule, but in a rock matrix there's not much place for the loose carbon to go, and it might as well recombine after a while.
At what rate will ionized amino acids in a rock matrix spontaneously shift handedness configuration? Is it different for different acids?
That sounds like a research project for somebody...