Active-site-directed inhibition of the plasma-membrane carrier transporting short-chain, neutral amino acids into Trypanosoma brucei.

1. Glycine chloromethyl inhibited the active-transport of L-serine into bloodstream forms of Trypanosoma brucei. 2. Substrates of the short-chain, neutral amino acid transport system (N1), but not of other amino acid transport systems, protected the carrier protein from inhibition. 3. Inhibition was never more than 80% complete. The residual activity might have due to a proportion of N1 carrier active sites which had not reacted with the inhibitor. 4. The inhibition was highly selective for the N1 amino acid transport system. Other amino acid transport systems were not affected and the rate of respiration was only slightly affected. 5. The inhibition was first-order with respect to concentration, indicating that one molecule of the inhibitor reacted with each carrier active-site. 6. The high selectivity of this inhibitor should make it a useful labelling agent during the isolation and purification of the N1 amino acid transport carrier protein(s).