Amino acids are not un-charged (lipid-soluble) substances. Why we might as well forget pyroglutamate as an amino acid.
Christensen
H N
HN
D000596:Amino Acids / Q000032:analysis*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D006801:Humans; D011760:Pyrrolidinones / Q000032:analysis*; D011761:Pyrrolidonecarboxylic Acid / Q000032:analysis* / Q000378:metabolism
D000596:Amino Acids; D011760:Pyrrolidinones; D011761:Pyrrolidonecarboxylic Acid