glutathione synthase gene Synthetase - an overview GLUTATHIONE SYNTHESIS - PMC
Description
Boobis AR, Fawthrop DJ, Davies DS, 1989

That works perfectly for insulin, which is standardized at known concentrations

doi: 10.1016/j.mib.2013.09.006

If a Klow listing does not tell you exactly what is inside, GHK-Cu is the more researchable option by default