Sensory receptors is the answer I found
A. Vili in stomach. And this is because of gluten.
Cation-exchange chromatography is used when the molecule of interest is positively charged, the stationary phase is negatively charged and positively charged molecules are loaded to be attracted to it. So, the amino acids with negative charge will elute the first. Glutamate, leucin, arginine is the order of elution because of their pI values ~3, ~6 ~10.