This bonded cysteine is also found in human breast milk, and can be replicated with raw cow's milk in the form of undenatured whey protein. (aminoacidstudies.org)
[2] Crowley DC, et al. «Safety and efficacy of undenatured type ll collagen in the treatment of osteoarthritis of the knee: a clinical trial.» (capsugel.com)
You have to be careful to pick the right kind of collagen supplement, though, as undenatured type II collagen is the only one that's been proven to significantly improve joint health. (legionathletics.com)