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Fig. 2 ASS1 deficiency is associated with citrulline accumulation and reduced concentration of ornithine. Wildtype zebrafish embryos were injected with either ASS1-targeting MO or mock at the 1-cell stage and subjected to quantitative analysis of amino acid concentrations applying HPLC at 1 dpf or 3 dpf, respectively. While concentrations of L-citrulline and L-ornithine were unaltered in response to MO-injection at developmental stage 1 dpf, ASS1-deficient zebrafish larvae exhibited a massive accumulation of L-citrulline at 3 dpf with concomitantly reduced concentration of L-ornithine (A, B), confirming impaired ASS1 function upon MO-injection. Notably, L-arginine concentrations remained unchanged at 1 and 3 dpf when compared to negative control (C). Data are expressed as μmol per g protein (A-C, whole body lysates, N = 3 with 50 larvae per group and experiment; Student's t-test, *P < 0.05).