Compound-specific isotope analysis of amino acids has widely been employed in various fields of studies to measure the trophic position of organisms in ecosystems. The size of elevation in the δ¹⁵N value of amino acids from diet to consumer species (i.e., TDF: trophic discrimination factor) is primarily driven by the flux of deamination, as a key factor, in consumers’ metabolism. However, the transamination (i.e., exchange of amino groups between amino acids) associated with the urea cycle (in amphibians and mammals) or uric acid cycle (in birds and reptiles) may be considered as another possible factor affecting the size of TDF (and its associated variation and/or diversity) in consumer species. In the present study, we conducted a controlled feeding experiment with a reptile, the leopard gecko Eublepharis macularius, to evaluate how the transamination associated with the uric acid cycle contributes to the size of TDF. The elevation in the δ¹⁵N value from diets to the gecko determined is 7.4‰ ± 0.3‰ and 0.6‰ ± 0.2‰ for glutamic acid and phenylalanine, respectively, and consequently, the TDFGlu/Phe calculated is 6.8‰± 0.1‰. These values fall in the range of general TDFs reported in previous studies (e.g., 7.6‰ ± 1.3‰). We demonstrate that the effects of ‘the transamination between amino acids associated with the uric acid cycle’ on the size of TDF are very small or substantially negligible, suggesting that the presence of urea or uric acid cycle is not always a considerable factor affecting the size of TDF of consumers.