Active‐Site‐Directed Inhibition of the Plasma‐Membrane Carrier Transporting Short‐Chain, Neutral Amino Acids into Trypanosoma brucei

Abstract

1 Glycine chloromethyl ketone 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 pro-portion of N1 carrier active sites which had not reacted with the inhibitor. 4 The inhibition was highly selective for the N, 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 activesite. 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).