L-Citrulline ELISA

Nitric oxide (NO) is a intra- and intercellular signaling molecule. It reacts with free radicals, metalloproteins and specific amino acid residues of proteins. NO plays an important role in the regulation of vascular tone. Endothelial NO (eNO) is produced by the vascular endothelium. It diffuses to neighboring vascular smooth muscle cells (VSMC), where NO activates soluble guanylate cyclase (sGC), which subsequently increases the intracellular cGMP production from GTP, and which in turn causes relaxation of smooth muscle and vasodilatation. Thus, functional changes of the endothelium in coronary artery disease may be an important factor in the development of vasospasm, ischaemia and thrombosis. L-citrulline as surrogate marker for NO. NO is synthesized in the citrullin-NO-cycle when L-arginine is oxidized to citrulline by NO synthase (NOS). In the second part of the urea cycle, arginine is re-synthesized from citrulline. The NOS catalyzed formation of L-citrulline and NO proceeds in two steps, whereby the product stochiometry of L-citrulline and NO is 1:1. Thus, the conversion of L-arginine to L-citrulline can be used as a surrogate marker for the NO synthesis. Pathologic high levels of citrulline serve as an indicator of nitrosative stress.

_{Knipp, M et al.Colorimetric 96-well Microtiter Plate Assay fort he Determination of Enzymatically Formed Citrulline. Analytical Biochemistry. 2000; 286: 257-264.}