Urine is a crucial diagnostic tool, revealing a wide range of disorders, but scientists have just uncovered one of its mysteries – how bodily fluid turns yellow.
A team of scientists from the University of Maryland and the US National Institutes of Health discovered that the color stems from a molecule made by bacteria in our digestive system.
It's an enzyme called bilirubin reductase (BilR), and it was the missing piece of the century-and-a-half-old puzzle that explains why urine is yellow.
The team also found that almost all healthy adults have BilR protein in their digestive systems, but many newborns and people with inflammatory bowel disease do not.
Urobilin gives urine its classic color. Doctors have known this for a long time, but they did not know which enzyme was responsible for the formation of urobilin
When blood cells reach the end of their life cycle at six months, they release an orange protein called bilirubin, which eventually turns into urobilin, the molecule responsible for coloring urine yellow.
Bilirubin is a waste product, and doctors generally consider it toxic.
some research It is suggested that it could help patients tolerate organ transplants, and perhaps even treat conditions such as strokes and multiple sclerosis.
It is passed into the digestive tract, where most of it is passed, but some of it is reabsorbed into the body.
The liver filters and absorbs as much of this excess as possible.
Hundreds of naturally occurring bacteria thrive in our digestive system, producing chemicals that help us break down foods to access their nutrients and get rid of waste products like bilirubin.
The authors of the new study found that nine of these bacteria break down bilirubin.
Three of them produce BilR, an enzyme that converts bilirubin into the molecules urobilinogen and stercobilinogen, which can be easily excreted in urine and feces.
Bilirubin reductase (BilR) is an enzyme produced by at least three different bacteria that naturally live in our intestines. The newly discovered enzyme is an important part of the chain of events that makes urine yellow. This specific type of BilR is produced by the bacteria Ruminococcus gnavus species
“Gut microbes encode the enzyme bilirubin reductase, which converts bilirubin into a colorless byproduct called urobilinogen,” said Brantley Hall, the study's lead author and an assistant professor of cell biology and molecular genetics at the University of Maryland. statement.
“Urobilinogen then spontaneously breaks down into a molecule called urobilin, which is responsible for the yellow color we are all familiar with.”
Scientists have known about urobilin since it was first discovered in 1868, 156 years ago.
But they knew nothing about BilR, the enzyme that helps make urobilin.
The results appeared in the journal Nature Microbiology.
“Now that we have identified this enzyme, we can begin to investigate how bacteria in our gut affect circulating bilirubin levels and related health conditions such as jaundice,” study co-author Xiaofang Jiang said in the statement.
Jaundice, characterized by yellowing of the skin and eyes, occurs when the liver cannot get rid of excess bilirubin.
“This discovery lays the foundation for understanding the gut-liver axis,” Jiang said.
Scientists have increasingly discovered that the gut microbiome, the collection of microbes that live in our digestive system, is linked to all kinds of health conditions, including depression, arthritis, and even aggression.
This new study adds another piece to understanding how the microbiome keeps us healthy.
“The multidisciplinary approach we were able to implement – thanks to collaboration between our laboratories – was key to solving the physiological mystery of why our urine appears yellow,” Hall said. “It is the culmination of many years of work by our team and highlights another reason why our gut microbiome is so vital to human health.”
(tags for translation) Daily Mail