The goal of Henri's thesis was to compare his knowledge of enzyme-catalysed reactions to the recognized laws of physical chemistry. Henri is credited with being the first to write the equation that is now known as the Michaelis-Menten equation. Using glucose and fructose in the catalytic reactions controlled by maltase and invertase, Leonor Michaelis was the first scientist to distinguish the different types of inhibition by using the pH scale which did not exist in Henri's time. Particularly during their work on describing the rate of this reaction they also tested and extrapolated on the idea of another scientist, Victor Henri, that enzyme they were using had some affinity for both products of this reaction – fructose and glucose. Using Henri's methods, Michaelis and Menten nearly perfected this concept of initial-rate method for steady-state experiments. They were studying inhibition when they found that non-competitive (mixed) inhibition is characterized by its effect on kcat (catalyst rate) while competitive is characterized by its effect on velocity (V). In the Michaelis and Menten experiments they heavily focused on pH effects of invertase using hydrogen ions. Invertase is an enzyme found in extracellular yeast and catalyzed reactions by hydrolysis or inverting a sucrose (mixture of sucrose and fructose) to “invert sugar.” The main reason for using invertase was that it could be easily assayed and experiments could be done in quicker manner. Sucrose rotates in polarimeter as dextroratatory-D whereas invert sugar is levorotatory-L. This made tracking the inversion of sugar relatively simple. They also found that α-D-glucose is released in reactions catalyzed by invertase which is very unstable and spontaneously changes to β-D-glucose. Although, these are both in the dextrorotatory form, this is where they noted that glucose can change spontaneously, also known as mutarotation. Failing to take this into consideration was one of the main reasons Henri's experiments fell short. Using invertase to catalyze sucrose inversion, they could see how fast the enzyme was reacting by polarimetry; therefore, non-competitive inhibition was found to occur in the reaction where sucrose was inverted with invertase. Terminology It is important to note that while all non-competitive inhibitors bind the enzyme at allosteric sites (i.e. locations other than its active site)—not all inhibitors that bind at allosteric sites are non-competitive inhibitors. In fact, allosteric inhibitors may act as competitive, non-competitive, or uncompetitive inhibitors. Many sources continue to conflate these two terms, or state the definition of allosteric