Determination of free and total cyst(e)ine in plasma of dogs and cats
Article first published online: 5 MAR 2008
Veterinary Clinical Pathology
Volume 33, Issue 4, pages 228–233, December 2004
How to Cite
Tôrres, C. L., Miller, J. W. and Rogers, Q. R. (2004), Determination of free and total cyst(e)ine in plasma of dogs and cats. Veterinary Clinical Pathology, 33: 228–233. doi: 10.1111/j.1939-165X.2004.tb00378.x
- Issue published online: 5 MAR 2008
- Article first published online: 5 MAR 2008
- cysteine oxidation;
Background: In human blood, the amino acid cysteine forms disulfide bonds with itself and with other sulfhydryl compounds in their free form and with sulfhydryls in protein. Protein-bound cysteine is lost when plasma proteins are removed before amino acid analysis. Objective: The purpose of this study was to assess the time course and extent of cyst(e)ine (cysteine + half-cystine) loss in dog and cat plasma.
Methods: An equal volume of 6% sulfosalicylic acid was added to plasma aliquots at 0,2,4,10,16,24, 36, 48, 60, and 72 hours after separation of blood cells. Tris-2-carboxyethyl-phosphine hydrochloride (TCEP-HC1), a reducing agent, was used to regenerate total plasma cyst(e)ine after 3 months of sample storage (−20°C).
Results: Initial free cyst(e)ine concentrations (mean ± SEM) were higher in canine plasma (77 ± 4 μmol/L) than in feline plasma (37 ± 3 μmol/L). Free plasma cyst(e)ine concentrations in dogs and cats decreased after first-order kinetics, with a half-life of 23 and 69 hours, respectively. Total plasma cysteine after TCEP-HC1 treatment was similar for dogs (290 μmol/L) and cats (296 μmol/L), but the percentage of free cysteine was higher (P = .02) in dogs (27%) than in cats (13%). Over half of the cyst(e)ine, homocysteine, cysteinylglycine, and glutathione were bound in vivo to plasma proteins. Conclusion: These results emphasize the importance of removing plasma proteins within 1 hour after blood collection for reliable assay of free plasma cyst(e)ine.