Cauxin

Cauxin is a carboxylesterase that is excreted in large amounts in cat urine. There is also evidence that it can serve as a peptide hydrolase in the production of cat pheromone precursors.[1][2] Cauxin has a mass of 70 kilodaltons and is composed of 545 amino acids.[3] The protein can also exist as a multimeric protein complex connected by disulfide bonds with a mass of 300-350 kilodaltons. This is its primary form in non-reducing conditions.[2][3] The proximal tubules of epithelial cells in the kidney express cauxin. This protein is secreted into the urine from the renal tubular cells.[4] The gene for the protein is also found in several other mammalian genomes in various organs. However, the only mammals that have cauxin present in urine are cats. It is also the first carboxylesterase to be found in urine.[3]

Cauxin has been shown to hydrolyze 3-methylbutanol-cysteinylglycine (3-MBCG) in the urine into felinine which then slowly degrades into the putative, sulfur-containing cat pheromone 3-mercapto-3-methylbutan-1-ol (MMB).[1] This pheromone is used to mark territory with urine.[1]

Neutered male cats have less cauxin in their urine than do intact males.[5] Intact males also have higher levels of cauxin than females and higher levels than kittens. This, in addition to cauxin's role in pheromone production, suggests that it is also involved in sexual signaling.[1]

Cauxin or its homologs are present in many cat species. These homologs are highly conserved and also exist as multimers. However, the cauxin concentrations in urine seems to vary depending on the species with larger species generally having lower concentrations in urine than smaller domestic cats. This is likely a result of decreased reliance on felinine, due to the existence of additional, more complex signaling molecules that are present in the urine of larger cats.[2]

Cauxin is also present in the seminal fluid of cats and several other mammals, including sheep, pigs, cattle, rams, boars, rats, and mice.[6][7] The cauxin found in seminal fluid is produced by epidydimal cells. The concentration in seminal fluid is much lower than its concentration of urine. The role of cauxin as an esterase allows it to hydrolyze specific monoacylglycerols, suggesting that it is involved in lipid transfer and metabolism. It is also theorized to play a role in fertilization.[6]

Cauxin protein from feline urine was reported in 2008 to act as a nucleator for struvite crystals, in an in vivo system containing magnesium, ammonium, and phosphate ions.[8] Thus, this protein may act as one cause for feline urinary stones.

Decreased cauxin concentration of urine is also a marker of tubulointerstitial nephritis in cats, a common illness in older domestic cats. This is due to damage to the tubular cells where excreted cauxin is produced.[9]

Chemistry

	→
Felinine	MMB

See also

• Cat pheromone

References

1. Miyazaki, Masao; Yamashita, Tetsuro; Suzuki, Yusuke; Saito, Yoshihiro; Soeta, Satoshi; Taira, Hideharu; Suzuki, Akemi (October 2006). "A Major Urinary Protein of the Domestic Cat Regulates the Production of Felinine, a Putative Pheromone Precursor". Chemistry & Biology. 13 (10): 1071–1079. doi:10.1016/j.chembiol.2006.08.013. PMID 17052611.
2. McLean, Lynn; Hurst, Jane L.; Gaskell, Christopher J.; Lewis, John C. M.; Beynon, Robert J. (2007-10-09). "Characterization of Cauxin in the Urine of Domestic and Big Cats". Journal of Chemical Ecology. 33 (10): 1997–2009. doi:10.1007/s10886-007-9354-6. ISSN 0098-0331. PMID 17924168.
3. Miyazaki, Masao; Yamashita, Tetsuro; Taira, Hideharu; Suzuki, Akemi (2008), Chemical Signals in Vertebrates 11, Springer New York, pp. 51–60, doi:10.1007/978-0-387-73945-8_4, ISBN 978-0-387-73944-1 Missing or empty |title= (help); |chapter= ignored (help)
4. Miyazaki, Masao; Yamashita, Tetsuro; Hosokawa, Masakiyo; Taira, Hideharu; Suzuki, Akemi (November 2006). "Species-, sex-, and age-dependent urinary excretion of cauxin, a mammalian carboxylesterase". Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology. 145 (3–4): 270–277. doi:10.1016/j.cbpb.2006.05.015. PMID 17045831.
5. Miyazaki, Masao; Kamite, Katsuyoshi; Soeta, Satoshi; Taira, Hideharu; Yamashita, Tetsuro (15 February 2003). "Molecular cloning and characterization of a novel carboxylesterase-like protein that is physiologically present at high concentrations in the urine of domestic cats (Felis catus)". Biochemical Journal. 370 (1): 101–110. doi:10.1042/bj20021446. PMC 1223137. PMID 12401131.
6. Miyazaki, Masao; Miyazaki, Tamako; Toyonaga, Mari; Tsutsui, Toshihiko; Taira, Hideharu; Yamashita, Tetsuro; Suzuki, Akemi (December 2011). "Characterisation of the carboxylesterase enzyme cauxin in the seminal fluid of the cat". The Veterinary Journal. 190 (3): 378–382. doi:10.1016/j.tvjl.2010.11.014. ISSN 1090-0233. PMID 21277238.
7. Ecroyd, Heath; Belghazi, Maya; Dacheux, Jean-Louis; Miyazaki, Masao; Yamashita, Tetsuro; Gatti, Jean-Luc (2006-02-01). "An Epididymal Form of Cauxin, a Carboxylesterase-Like Enzyme, Is Present and Active in Mammalian Male Reproductive Fluids1". Biology of Reproduction. 74 (2): 439–447. doi:10.1095/biolreprod.105.046847. ISSN 0006-3363. PMID 16251497.
8. Matsumoto, Kayo; Funaba, Masayuki (February 2008). "Factors affecting struvite (MgNH4PO4·6H2O) crystallization in feline urine". Biochimica et Biophysica Acta (BBA) - General Subjects. 1780 (2): 233–239. doi:10.1016/j.bbagen.2007.09.013. PMID 17976920.
9. Miyazaki, Masao; Soeta, Satoshi; Yamagishi, Norio; Taira, Hideharu; Suzuki, Akemi; Yamashita, Tetsuro (February 2008). "Tubulointerstitial nephritis causes decreased renal expression and urinary excretion of cauxin, a major urinary protein of the domestic cat". Research in Veterinary Science. 82 (1): 76–79. doi:10.1016/j.rvsc.2006.06.009. ISSN 0034-5288. PMID 16919690.