Every animal must urinate to get rid of liquid waste in their body. While the pee of a healthy person has a distinctly yellow color, it’s been unclear to scientists for centuries what actually gives urine this hue. Now, a team from the University of Maryland and National Institutes of Health believe that they have solved this mystery by pinpointing the microbial enzyme that makes our pee yellow. The findings are detailed in a study published January 3 in the journal Nature Microbiology.
[Related: Renaissance-era doctors used to taste their patients’ pee.]
According to study co-author and University of Maryland microbiologist Brantley Hall, the team built on decades of research going back to the 1960s and a difficult three-and-a-half-year long lab experiment to find that an enzyme in the gut microbiome called bilirubin reductase is responsible for urine’s color.
“The gut microbiome is just full of incredible chemists. It’s so important to human physiology, all these molecules that the gut microbes are making,” Hall tells PopSci. “As we understand more about microbial chemistry in our gut, we’re going to understand the important things. But the first step for any of this is to figure out the enzymes responsible. If you don’t know what’s going on, you basically can’t even start with the research.”
Solving a microbial mystery
Previously, scientists knew that the yellow color comes from how the body gets rid of old blood cells. Red blood cells typically reach the end of their life cycle after about 120 days and they are degraded in the liver. A byproduct of this process called bilirubin is a bright orange substance that is secreted from the liver and into the gut. Bacteria living in the gut then convert bilirubin into a colorless substance called urobilinogen. The urobilinogen is finally degraded into the yellow pigment molecule called urobilin that plays a part in the coloring. What scientists did not know was the…
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