Wee Mystery Solved

Researchers at UMD and the National Institutes of Health have identified the enzyme responsible for making urine yellow, and it’s more than a matter of idle curiosity or grade-school giggles.

The discovery of bilirubin reductase, introduced in a study published in the journal Nature Microbiology, paves the way for further research into the gut microbiome’s role in ailments like jaundice and inflammatory bowel disease. It also brings scientists closer to a holistic understanding of how the gut’s resident microorganisms contribute to overall health.

Red blood cells release a bright orange pigment, bilirubin, as they grow old and degrade. The newly described enzyme, produced by gut microbes, initiates bilirubin’s two-step breakdown into the chemical that gives urine its characteristic hue.

“It’s remarkable that an everyday biological phenomenon went unexplained for so long,” says lead author Brantley Hall, an assistant professor in the university’s Department of Cell Biology and Molecular Genetics.