The transport and metabolism of alanine by Giardia intestinalis

Mol Biochem Parasitol. 1993 Sep;61(1):49-57. doi: 10.1016/0166-6851(93)90157-s.


The transport and metabolism of L-alanine by Giardia intestinalis trophozoites was characterised. G. intestinalis formed 14CO2 from L-[1-14C]alanine (1 mM) at a rate of 4.8 nmol min-1 (mg protein)-1 at 30 degrees C. The system was saturable, with an apparent Km of 0.29 mM for alanine, and a maximal rate of 6.1 nmol min-1 (mg protein)-1. L-cycloserine inhibited the metabolism, as did a number of amino acids including glycine, serine and threonine. D-alanine and 2-aminoisobutyrate had no effect. G. intestinalis was shown to have a functional transport system for L-alanine. The transporter was saturable with a Km of 1.5 mM and a maximal velocity of 6.1 nmol min-1 (mg protein)-1 at 23 degrees C. It was temperature dependent, with a Q10 of 2.2 and activation energy of 15.9 kcal mol-1. It was not inhibited by potential inhibitors of energy dependent transport. Glycine, L-serine and L-threonine potently inhibited L-alanine transport, whereas D-alanine, beta-alanine and 2-aminoisobutyrate had no effect. L-serine competitively inhibited L-alanine influx. In trophozoites preloaded with [3H]alanine, rapid exchange occurred with external L-alanine and L-serine, but not with D-alanine confirming that L-alanine and L-serine share a common transport site. These observations indicate that G. intestinalis has a functional alanine transporter, which may be an antiport catalysing the exchange of alanine, serine, glycine and threonine.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alanine / metabolism*
  • Animals
  • Biological Transport
  • Giardia lamblia / metabolism*
  • Serine / metabolism
  • Temperature


  • Serine
  • Alanine