One day the mouse cage was place next to the stove heating the room, and they observed the mice going into convulsions. Winters in Copenhagen were very cold and the laboratories did not have HVAC (heating ventilating, and air conditioning) like laboratories do today. Instead each room was heated, or more accurately, partially heated by a stove. In the usual placement of the mouse cage, the mice were a bit chilly. Professor Krogh and his students found that mice have a temperature dependent response to low blood glucose levels. The mice were moved to an incubator and the insulin purification carried on.
The young student Detlev Müller played a small, unimportant, role in the insulin purification. He merely administered the insulin to the mice and recorded the reaction. He joined the team after some others had already discovered the temperature dependent nature of the mouse’s hypoglycemic reaction. He did have the opportunity to witness a miraculous recovery of a patient.
One patient was in a coma at the local hospital, the Kommune Hospital. The specialist in diabetes, Dr Sophus Bang, did not believe in insulin. Dr Bang thought he would try the new insulin on this man, since no possible harm could come from administering a substance to a man about to die. Shortly after administering the insulin, the man rose up in his bed, opened his eyes and stared straight into Dr Bang’s eyes, creating a new believer in insulin and leaving a life long impression on Detlev Muller.
Detlev only spent a few months as a laboratory assistant for Professor Krogh. His scientific interests were in studying plants. Although he admired the new insulin technology, he thought his life’s work would be more abstract: observing and classifying plants and molds.
By 1928, Detlev Müller was a young professor of plant physiology at University of Copenhagen. He was studying the common fungus, Aspergillus niger. This fungus can be found everywhere, often growing on plants. It is even a frequent source of human ear infections.
While Müller was growing his fungus, he noted that under some circumstances bacteria could not grow adjacent to this fungus. Upon closer study, he found that bacteria could not grow in the vicinity of the fungus, only when glucose was present. This was the same year that Alexander Fleming first isolated penicillin, so Müller may have been searching for antibiotics, perhaps dreaming of recreating the life-saving experience he had witnessed with insulin.
If he was searching for an antibiotic, he was probably disappointed. He found instead that the bacteria couldn’t grow because of the fungus was somehow producing hydrogen peroxide. Müller went on to isolate an enzyme secreted by the fungus, glucose oxidase. This enzyme catalyzes the reaction of glucose into hydrogen peroxide. Although glucose oxidase was not a suitable antibiotic, it eventually became an important enzyme for the measurement of glucose in blood.