During the period from 1876 till 1881 Arthur Harden attended Tettenhall College. Four years later, in 1885, he attained a degree in chemistry with first-class honors, graduating from Owen College, now the University of Manchester. In 1888 Harden obtained Doctor of Philosophy degree at the University of Erlangen-Nuremberg. Some time later, in 1902, he got Doctor of Science degree from the Victoria University.
After unsuccessfully applying for jobs as a private school principal and as an inspector, Harden was appointed a professor of biochemistry in 1897 at the British Institute of Preventative Medicine (renamed a year later to the Jenner Institute and, in 1903, the Lister Institute), a post he held till 1912. Two years later, in 1914, Arthur served as a director of the institute.
While the institute staff taught students pursuing careers as public health officers, testing water for city officials and otherwise doing little scientific research, Harden was hired at Roscoe’s suggestion to teach chemistry and bacteriology. As medical schools began to offer the same subjects, Harden’s classes were phased out and the head of the bacteriology department recommended him to consider research. Fermentation, or the breakdown of sugar by bacteria, became Harden’s objective as he set upon discovering a chemical means of distinguishing various fermentation patterns in the bacteria Escherichia coli. Harden was able to show that the ratio of alcohol to acetic acid, two of the compounds formed during bacterial fermentation, was a useful guide in determining which variety of the bacterium was involved in a given fermentation process.
The year Harden arrived at the institute, Eduard Buchner had released his revolutionary research on fermentation. Buchner had discovered that fermentation could take place in the absence of living yeast cells, yielding an enzyme he named zymase. Although the reaction took longer than it would have had live cells been present, it produced the familiar end products of fermentation, carbon dioxide and alcohol. Buchner’s experiment was the first evidence of the existence of enzymes. Like many others in the scientific community, Harden began to build on Buchner’s work. He showed that fermentation could occur because zymase acted on glycogen (a sugar) that had been within the cells themselves. Assisted by William Young, Harden made significant discoveries about the role of phosphate in fermentation over the next decade.
In 1904 Harden put a semipermeable membrane bag full of yeast extract into pure water. Harden knew that the molecules, densely packed inside the bag, would move through the membrane into the water because of the lower density of yeast outside of the bag. He also knew that the membrane would allow only molecules of a given size to pass through — a process called dialysis. Zymase stopped breaking down the sugar inside the bag while reintroducing water from outside the bag which contained the small molecules that had diffused out through the membrane. When Harden boiled the yeast extract, it failed to cause fermentation at all, indicating that zymase actually consisted of two parts. Because zymase lost its activity after dialysis, he decided that the larger part remained trapped inside the bag. This, together with its loss of effectiveness led Harden to conclude that the larger part was probably a protein, the smaller part (having not perished during boiling), a nonprotein.
Pursuing the matter further, Harden and Young added boiled yeast juice to an ongoing fermentation and measured the amount of carbon dioxide released. Although all active agents should have been destroyed by the boiling, the addition sped up the process. They discovered the boiled juice contained a phosphate substance called cozymase. Harden’s work showed that three factors are necessary for fermentation to occur: the ferment, the enzyme and a coenzyme. By attending to the entire fermentation process — not only the end products as had been the previous practice— he laid the important groundwork for further understanding of metabolic processes, such as ossification.
In 1906 Harden founded Biochemical Journal together with William Bayliss. In 1912 the scientist became a co-editor of the Biochemical Journal, a position he held till 1937.
During the period from 1912 to 1930, Arthur served as a professor of biochemistry at the University of London.
The scientist also contributed to journals and periodicals, including Transactions of the Manchester Literary and Philosophical Society and Proceedings of the Royal Society.
Arthur married Georgina Sydney Bridge in 1900. The woman died in 1928.