Determination of free and total cyst(e)ine in plasma of dogs and cats.

Abstract

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 - HCl), a reducing agent, was used to regenerate total plasma cyst(e)ine after 3 months of sample storage (-20 degrees C).

RESULTS:

Initial free cyst(e)ine concentrations (mean +/- SEM) were higher in canine plasma (77 +/- 4 micromol/L) than in feline plasma (37 +/- 3 micromol/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 - HCl treatment was similar for dogs (290 micromol/L) and cats (296 micromol/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.

• Authors: Cristina L Tôrres, Joshua W Miller, Quinton R Rogers
• Journal: Veterinary clinical pathology (Vet Clin Pathol) Vol. 33 Issue 4 Pg. 228-33 ( 2004) ISSN: 0275-6382 [Print] United States
• PMID: 15570560 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Dipeptides
• Phosphines
• Reducing Agents
• Homocysteine
• tris(2-carboxyethyl)phosphine
• cysteinylglycine
• Cystine
• Glutathione
• Cysteine

Topics

• Animals
• Cats (blood)
• Cysteine (blood)
• Cystine (blood)
• Dipeptides (blood)
• Dogs (blood)
• Glutathione (blood)
• Homocysteine (blood)
• Male
• Phosphines
• Reducing Agents
• Time Factors