L-cystine is the disulfide form of L-cysteine, and is an amino acid found in a variety of frequently consumed protein sources. I have read that it helps protect against damage from radiation and alcoholism, and is essential in the formation of hair and skin. The amino acid profile on the milk-based protein powder I have states that it contains 278mg per 28g serving. So, I don't know whether it's ever synthesized or merely isolated. You might be able to find it sold as an individual amino acid at a health food store and locate the number of the manufacturer. I have found those places to be very straight-forward about their methods.
L-cysine
Re: L-cysine
