This might be due to unfavourable ionisation properties of the disulfide-containing peptide or the disulfide might negatively affect tryptic cleavage of the respective peptide before mass spectrometric analysis
In a technical sense, it is a tripeptide made of three amino acids that acts like a cellular magnet for toxins
GSH deficiency in cell culture studies induced oxidative stress, leading to the downregulation of VDBP/VD-25-hydroxylase/VDR, and upregulation of CYP24A1 in hepatocytes
Ritelli M, Dordoni C, Venturini M, Chiarelli N, Quinzani S, Traversa M, Zoppi N, Vascellaro A, Wischmeijer A, Manfredini E, Garavelli L, Calzavara-Pinton P, Colombi M
Not all supplements (even those marketed for PMS relief) are rooted in science, though