The uptake and conversion of l-[U¹⁴C-] aspartate and l-[U¹⁴C-] alanine to ¹⁴CO₂ by intact trophozoites of Giardia duodenalis

1. 1. Intact trophozoites of Giardia duodenalis (clone P1C10) took up and metabolised l-[U¹⁴C-] aspartate to ¹⁴CO₂ at rates of 10.27 ± 0.76 and 27.6 ± 2.07 hr^-1 10^-6 cells in a simple maintenance medium (MM) and in a complex bile supplemented (BIS-33) medium respectively. 2. 2. Intact trophozoite of G. duodenalis (clone P1C10) also took up and metabolised l-[U¹⁴C-] alanine to ¹⁴CO₂ at rates of 20.6 ± 1.1 and 91.4 ± 17.5 ng hr 10^-6 cells in t simple (MM) and complex (BIS-33) medium respectively. 3. 3. trophozoite sonicates contained significant levels of aspartate-2-oxoglutarate transaminase (AST; EC 2.6.1.1) and alanine-2-oxoglutarate transaminase (ALT; EC 2.6.2.2.). Specific activities (at 23°C) were 95.1 ± 11.3 and 87.3 ± 9.8 nmol (min)-1 (mg protein)-1 respectively. 4. 4. These observations suggests that Giardia has the capacity to utilise aspartate and alanine and possibly other amino acids as alternative sources of energy. 5. 5. The extrusion or uptake of alanine by Giardia trophozoites may be dictated by the intracellular redox-status of the protozoan parasite or components in the external mileu.