the opioid pentapeptides leu- and met-enkephalin specifically inhibit the uptake of these three imino/amino acids , presumably by interaction with a nonopioid receptor , since the inhibition is not affected by the opiate antagonist naloxone and occurs with des-tyrosyl enkephalins as well as with the intact pentapeptides .
C0014295
met-enkephalin
C0014298
enkephalins