Ever wondered why urine appears yellow? According to a study published Wednesday in the journal Nature Microbiology, researchers have pinpointed the enzyme accountable for the colour of urine, finally solving a longstanding mystery that has perplexed scientists for years.
“Remarkably, an everyday biological phenomenon went unexplained for so long, and our team is excited to be able to explain it,” Brantley Hall, an assistant professor in the University of Maryland’s Department of Cell Biology and Molecular Genetics, said in a news statement.
Urine comprises water, electrolytes, and waste substances filtered by your kidneys from the bloodstream. Over 125 years ago, scientists identified urobilin as the yellow hue in urine but lacked knowledge about its production’s origin.
Recent findings reveal a connection between urine colour and the body’s red blood cells. As red blood cells break down, they generate a vibrant orange pigment known as bilirubin. Ordinarily, this pigment gets discharged into the digestive system, where it might be excreted or partially reabsorbed. Upon reaching the gut, the intestinal microorganisms can transform bilirubin into different molecules, as indicated by the study.
“Gut microbes encode the enzyme bilirubin reductase that converts bilirubin into a colourless byproduct called urobilinogen,” Hall, the study’s lead author, said. “Urobilinogen then spontaneously degrades into a molecule called urobilin, which is responsible for the yellow colour we are all familiar with.”
The researchers said that before the study, the scientists thought there were multiple enzymes involved, rather than a single enzyme.
Now, researchers said that the discovery of the bilirubin reductase enzyme could help researchers learn more about gut health, inflammatory bowel disease and jaundice.
The researchers said that enzymes are present in almost all healthy adults, but are missing from newborns and people with inflammatory bowel disease.
“Now that we’ve identified this enzyme, we can start investigating how the bacteria in our gut impact circulating bilirubin levels and related health conditions like jaundice,” study co-author and National Institutes of Health investigator Xiaofang Jiang said. “This discovery lays the foundation for understanding the gut-liver axis.”