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. Author manuscript; available in PMC: 2015 Oct 1.
Published in final edited form as: Acta Paediatr. 2014 Jun 20;103(10):1019–1026. doi: 10.1111/apa.12707

Figure 1.

Figure 1

Model for L-citrulline transport, arginine channelling and nitric oxide (NO) metabolism in pulmonary endothelial cells. Circulating L-citrulline is taken up by the sodium-dependent neutral amino acid transporter, SNAT1, and is delivered to a multi-protein complex containing the urea cycle enzymes, argininosuccinate synthetase, ASS, and argininosuccinate lyase, ASL, endothelial nitric oxide synthase, eNOS, and the chaperone protein, heat shock protein 90, Hsp90, for efficient metabolism of L-citrulline to arginine and arginine to NO and L-citrulline. This model would explain the so called arginine paradox and would predict that citrulline is an effective precursor for NO production.