On this page
Every NEET biology student meets a curve that rises steeply and then flattens: the rate of an enzyme reaction against substrate concentration. The equation behind that curve carries two names, Michaelis and Menten. This post covers who they were, what their 1913 experiment measured, and how to use the equation with real numbers.
Who were Leonor Michaelis and Maud Menten?
Leonor Michaelis was a Berlin biochemist with an unusual career. A biographical essay by James R. Wright Jr. in Pediatric and Developmental Pathology explains that, though internationally known, he never held an academic post in Germany, which the essay links to antisemitism. He ran the laboratories of the Berlin Municipal Hospital from 1906 to 1922 and did research in a small laboratory there. He later worked in Japan, at Johns Hopkins and, from 1929, at the Rockefeller Institute. He died in 1949, aged 74.
Maud Menten was Canadian. The Dictionary of Canadian Biography records that she was born on 20 March 1879 in Lambton County, Ontario, and died on 17 July 1960 in Leamington, Ontario. As a child in British Columbia she travelled by canoe and pony to reach school. Wright's essay adds that she earned her medical degrees at the University of Toronto (1907 and 1911) and a PhD in biochemistry at the University of Chicago (1916), then spent decades as a pathologist in Pittsburgh.
How did Menten end up in Berlin?
In 1912, according to Wright, Menten sailed to Europe, months after the Titanic sank, and worked for about a year in Michaelis's laboratory. She was 33. Michaelis was known for acid-base chemistry, and she had been citing his work for years. Their joint paper on invertase was submitted on 4 February 1913, when she had been in Berlin for at most about six months. Exactly who did which experiments is not recorded, and Wright notes that the paper itself is almost the only document of her time there.
What did their experiment measure?
The enzyme was invertase, which splits sucrose into glucose and fructose. The reaction changes how the sugar solution rotates polarised light, so they could follow it with a polarimeter, reading the change in rotation each minute.
Kenneth Johnson and Roger Goody translated the 1913 paper into English for its centenary, and their account in Biochemistry highlights three things:
They measured initial rates. Glucose and fructose slow the enzyme down, so Michaelis and Menten timed the reaction only at the start, before products could build up.
They fixed earlier mistakes. Victor Henri had already proposed an enzyme-substrate complex. But, as the paper pointed out, he did not allow for the slow change between two forms of glucose after the reaction (mutarotation) and did not control acidity. Michaelis and Menten handled both.
They proposed a mechanism. The rate, they argued, is proportional to the concentration of the sucrose-enzyme complex. From their initial rates they estimated a dissociation constant for sucrose of 16.7 mM.
Johnson and Goody also re-analysed the original data with modern software and found "an unanticipated rigor and precision". The pair had even fitted full time-course data, including the products' inhibition, to a single constant.
What does the equation say?
In modern form, v = Vmax[S] / (Km + [S]), where v is the initial rate, [S] is the substrate concentration, Vmax is the rate when the enzyme is saturated and Km is the substrate concentration at which v is half of Vmax. Your NCERT Class 11 Biology chapter on biomolecules shows this curve in Figure 9.5, with Vmax/2 and Km marked, and explains that the rate stops rising once all enzyme molecules are saturated.
The modern version owes something to a later paper. In 1925 G. E. Briggs and J. B. S. Haldane published "A Note on the Kinetics of Enzyme Action", which Johnson and Goody credit with introducing the steady-state approach used today.
Worked example: using Km = 16.7 mM
Take Km = 16.7 mM, the sucrose value above, and call Vmax 100 units (a sample number for practice).
At [S] = 16.7 mM: v = 100 × 16.7 / (16.7 + 16.7) = 100 × 0.5 = 50 units. At [S] = Km you always get half of Vmax.
At [S] = 50 mM: v = 100 × 50 / (16.7 + 50) = 5000 / 66.7 = 75.0 units.
At [S] = 5 mM: v = 100 × 5 / 21.7 = 23.0 units.
What [S] gives 90 units? Set 90 = 100[S] / (16.7 + [S]). Then 90 × 16.7 + 90[S] = 100[S], so 1503 = 10[S] and [S] = 150.3 mM. That is 9 × Km.
The last line is the useful surprise. Going from half speed to 90 per cent speed needs nine times more substrate, not twice as much. That is why the curve flattens so slowly.
What mistakes do students make?
Calling Km the substrate concentration at Vmax. It is the concentration at half of Vmax. The curve never truly reaches Vmax.
Thinking a bigger Km means a better enzyme. A smaller Km means the enzyme reaches half speed at lower substrate concentration, which usually signals tighter binding.
Forgetting the conditions. NCERT stresses that temperature and pH also change activity. Michaelis and Menten got clean results partly because they controlled acidity.
When a rearrangement like the last one trips you up, the Fermi Problem Library has a step-by-step solver that explains the reasoning, so you can see which rearrangement went wrong. For the rest of the chapter, use our guide to enzymes for NEET biology, and for the earlier discovery that enzymes work outside cells, read about Eduard Buchner's yeast juice.
What can a student take from how they worked?
Measure before things get messy. Timing only the start of the reaction removed the product problem instead of fighting it.
Read your predecessors critically. Henri had the right idea but uncontrolled conditions. Finding his two errors was half the discovery.
Go where the expertise is. Menten crossed an ocean to learn from Michaelis.
Next step: calculate v at [S] = 2Km and [S] = 4Km yourself, then check that you get two-thirds and four-fifths of Vmax.
