Cauxin is a

carboxylesterase The enzyme carboxylesterase (or carboxylic-ester hydrolase, EC 3.1.1.1; systematic name carboxylic-ester hydrolase) catalyzes reactions of the following form: :a carboxylic ester + H2O \rightleftharpoons an alcohol + a carboxylate Most enzymes fr ...

that is excreted in large amounts in

cat urine The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of t ...

. There is also evidence that it can serve as a peptide hydrolase in the production of cat pheromone precursors. Cauxin has a mass of 70 kilodaltons and is composed of 545

amino acids Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

. The protein can also exist as a

multimeric In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relativ ...

protein complex connected by disulfide bonds with a mass of 300-350 kilodaltons. This is its primary form in non-reducing conditions. The proximal tubules of epithelial cells in the kidney express cauxin. This protein is secreted into the urine from the renal tubular cells. 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. Cauxin has been shown to

hydrolyze Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis i ...

3-methylbutanol-cysteinylglycine (3-MBCG) in the urine into

felinine Felinine, also known as ''(R)-2-amino-3-(4-hydroxy-2-methylbutan-2-ylthio)propanoic acid'', is a chemical compound and amino acid found in cat urine and a precursor via microbial lyase of the putative cat pheromone and thiol called 3-mercapto-3-me ...

which then slowly degrades into the putative, sulfur-containing

cat pheromone A cat pheromone is a chemical molecule, or compound, that is used by cats and other felids for communication. These pheromones are produced and detected specifically by the body systems of cats and evoke certain behavioural responses. The name of ...

3-mercapto-3-methylbutan-1-ol 3-Mercapto-3-methylbutan-1-ol, also known as MMB, is a thiol and an alcohol. MMB is a degradation product of the amino acid felinine in cat urine and is a cat pheromone. MMB is also found in Sauvignon blanc wines together with the related compound ...

(MMB). This pheromone is used to mark territory with urine. Neutered male cats have less cauxin in their urine than do intact males. 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. 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. Cauxin is also present in the

seminal fluid Semen, also known as seminal fluid, is an organic bodily fluid created to contain spermatozoa. It is secreted by the gonads (sexual glands) and other sexual organs of male or hermaphroditic animals and can fertilize the female ovum. Semen is ...

of cats and several other mammals, including sheep, pigs, cattle, rams, boars, rats, and mice. 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 Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...

. 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. Thus, this protein may act as one cause for feline urinary stones. Decreased cauxin concentration of urine is also a marker of

tubulointerstitial nephritis Interstitial nephritis, also known as tubulointerstitial nephritis, is inflammation of the area of the kidney known as the renal interstitium, which consists of a collection of cells, extracellular matrix, and fluid surrounding the renal tubules. ...

in cats, a common illness in older domestic cats. This is due to damage to the tubular cells where excreted cauxin is produced.

Chemistry

References

{{Portal bar, Biology, border=no Proteases EC 3.4

Chemistry

See also

References