L-Arginine is the only biological substrate of nitric oxide synthase in a reaction yielding NO and L-citrulline as co-products. The resynthesis of L-arginine from L-citrulline has been observed in murine macrophages. However, it is not known whether avian macrophages have a similar capacity for the synthesis of arginine. The present studies were carried out to determine whether L-citrulline can support NO (measured as nitrite) production in the HD11 cell, a chicken macrophage cell line. When added to media lacking L-arginine, L-citrulline supported a low level of nitrite accumulation: about 4 to 11% of the amount of nitrite formed from an equivalent concentration of L-arginine. Aspartic acid was not limiting for NO production from citrulline.
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