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L-Citrulline is a non-essential amino acid that is synthesized from ornithine and carbamoyl phosphate in the urea cycle. It is first isolated from watermelon. It can act as a nitric oxide synthase inhibitor.
Nutritional supplement in health care products.

L-Amino Acids
Catalog number
CAS number
Molecular Formula
Molecular Weight
(2S)-2-amino-5-(carbamoylamino)pentanoic acid
Citrulline; H-Cit-OH; Delta-Ureidonorvaline; Sitrulline; (2S)-2-amino-5-(carbamoylamino)pentanoic acid
White Crystalline Powder
Melting Point
220-221°C (dec.)
Store at RT
Ingredient of health care products.
InChI Key
Canonical SMILES
1.Formation and reactions of the heme-dioxygen intermediate in the first and second steps of nitric oxide synthesis as studied by stopped-flow spectroscopy under single-turnover conditions.
Boggs S;Huang L;Stuehr DJ Biochemistry. 2000 Mar 7;39(9):2332-9.
To better understand the mechanism of nitric oxide (NO) synthesis, we studied conversion of N-hydroxy-L-arginine (NOHA) or L-arginine (Arg) to citrulline and NO under single-turnover conditions using the oxygenase domain of neuronal nitric oxide synthase (nNOSoxy) and rapid scanning stopped-flow spectroscopy. When anaerobic nNOSoxy saturated with H(4)B and NOHA was provided with 0.5 or 1 electron per heme and then exposed to air at 25 degrees C, it formed 0.5 or 1 mol of citrulline/mol of heme, respectively, indicating that NOHA conversion had 1:1 stoichiometry with respect to electrons added. Identical experiments with Arg produced substoichiometric amounts of NOHA or citrulline even when up to 3 electrons were provided per heme. Transient spectral intermediates were investigated at 10 degrees C. For NOHA, four species were observed in the following sequence: starting ferrous nNOSoxy, a transient ferrous-dioxygen complex, a transient ferric-NO complex, and ferric nNOSoxy.
2.Two different approaches to restore renal nitric oxide and prevent hypertension in young spontaneously hypertensive rats: l-citrulline and nitrate.
Chien SJ;Lin KM;Kuo HC;Huang CF;Lin YJ;Huang LT;Tain YL Transl Res. 2014 Jan;163(1):43-52. doi: 10.1016/j.trsl.2013.09.008. Epub 2013 Oct 8.
Nitric oxide (NO) deficiency mediates oxidative stress in the kidney and is involved in the development of hypertension. NO synthesis occurs via 2 pathways: nitric oxide synthase (NOS) dependent and NOS-independent. We tested whether the development of hypertension is prevented by restoration of NO by dietary l-citrulline or nitrate supplementation in young spontaneously hypertensive rats (SHRs). Male SHRs and normotensive Wistar Kyoto control rats (WKYs)s age 4 weeks were assigned to 4 groups: untreated SHRs and WKYs, and SHRs and WKYs that received 0.25% l-citrulline for 8 weeks. In our second series of studies, we replaced l-citrulline with 1 mmol/kg/d sodium nitrate. All rats were sacrificed at age 12 weeks. We found an increase in the blood pressure of SHRs was prevented by dietary supplementation of l-citrulline or nitrate. Both treatments restored NO bioavailability and reduced oxidative stress in SHR kidneys. l-Citrulline therapy reduced levels of l-arginine and asymmetric dimethylarginine (ADMA)-an endogenous inhibitor of NOS-and increased the l-arginine-to-ADMA ratio in SHR kidneys.
3.Effect of Exogenous Proline on Metabolic Response of Tetragenococcus halophilus under Salt Stress.
He G;Wu C;Hunag J;Zhou R J Microbiol Biotechnol. 2017 Sep 28;27(9):1681-1691. doi: 10.4014/jmb.1702.02060.
This study investigated the effect of proline addition on the salt tolerance of ;Tetragenococcus halophilus;. Salt stress led to the accumulation of intracellular proline in ;T. halophilus;. When 0.5 g/l proline was added to hyperhaline medium, the biomass increased 34.6% (12% NaCl) and 27.7% (18% NaCl) compared with the control (without proline addition), respectively. A metabolomic approach was employed to reveal the cellular metabolic responses and protective mechanisms of proline upon salt stress. The results showed that both the cellular membrane fatty acid composition and metabolite profiling responded by increasing unsaturated and cyclopropane fatty acid proportions, as well as accumulating some specific intracellular metabolites (environmental stress protector). Higher contents of intermediates involved in glycolysis, the tricarboxylic acid cycle, and the pentose phosphate pathway were observed in the cells supplemented with proline.
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