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Invertase is an enzyme that hydrolyses sucrose into glucose and fructose. Its name reflects the change in optical rotation of the sugar mixture during the reaction. Optical rotation therefore provides a measurable signal of chemical conversion, provided other contributions to that signal are controlled. ^[ref]

The classic kinetic study measured initial reaction rates at different sucrose concentrations. At low substrate concentration the rate rises strongly as more substrate is supplied; at high concentration the finite amount of enzyme limits the rate. This supplies a concrete motivation for Michaelis-Menten kinetics. Product mutarotation complicates the optical readout, showing why a convenient physical signal is not automatically a direct count of reaction events.

L. Michaelis coauthored the 1913 invertase study with Maud L. Menten. Their interpretation connected the substrate dependence of reaction speed to reversible enzyme-substrate binding followed by conversion to product. At high substrate concentration, occupation of the finite enzyme population limits the rate, giving the saturation behavior associated with Michaelis-Menten kinetics.^[ref]

The original equilibrium-binding argument should be distinguished from the later quasi-steady-state derivation of the same rate-law shape. Fitting that shape alone does not distinguish every possible microscopic mechanism. The Rockefeller Archive Center's identified 1946 portrait records the scientist as Leonor Michaelis.

Maud L. Menten coauthored the 1913 study of invertase that underlies Michaelis-Menten kinetics. The experiment followed changes in optical rotation as sucrose was hydrolysed, controlling acidity and accounting for the sugars' mutarotation. These controls mattered because the instrument observed a changing optical signal rather than the reaction rate directly. The resulting comparison of initial rates across substrate concentrations connected a measurable saturation curve to an enzyme-binding model.^[ref]

The Michaelis-Menten equation describes a saturating enzyme reaction rate:Here $s$ is free substrate concentration, $V_{\max }$ is the limiting rate at large $s$, and the Michaelis constant $K_M$ is the concentration giving $v=V_{\max }/2$.

For the elementary mechanism $E+S\rightleftharpoons ES\to E+P$, use binding rate constant $k_1$, dissociation rate constant $k_{-1}$ and turnover number $k_{\mathrm{cat}}$. The quasi-steady-state approximation sets the fast enzyme-substrate complex balance towhere $e_T$ is total enzyme concentration and $c=[ES]$. Solving givesThis modern steady-state derivation does not require substrate binding to be in chemical equilibrium. In particular, $K_M$ is not generally the binding dissociation constant.

At $s\ll K_M$, $v\simeq (V_{\max }/K_M)s$; at $s\gg K_M$, the enzyme approaches saturation. The simple model assumes an appropriate timescale separation and negligible reverse product reaction; additional binding sites or inhibition can change the rate law.

L. Michaelis and Maud L. Menten investigated invertase acting on sucrose. They compared early reaction rates at different substrate concentrations using optical rotation, controlled temperature and acidity, and accounted for the separate optical change caused by sugar mutarotation. These controls helped distinguish catalytic conversion from changes in the measurement signal. ^[ref]