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To be honest I know very few about enzymes and absolutely nothing about Michaelis–Menten. However, when I "took the Michaelis-Menten equation, replaced v with 0.4Vmax, canceled the Vmaxes (one on each side), and solved for [S]", my result is positive: 0.4 * Vmax = S * Vmax / ( Km + S ) 0.4 = S / ( Km + S ) S = 0.4 * Km + 0.4 * S 0.6 * S = 0.4 * Km S = Km * ...


3

Have you heard of something known as "Occam's Razor" ? It says when you have multiple possible explanations/hypotheses then select the one which is simplest (i.e least number of assumptions) Same with mathematical models. Chemical kinetics models usually assume first order unless there is some evidence against it. Similarly, for enzyme kinetics, as long ...


2

This expands my comment on the question to an answer. If an enzyme exhibits Michaelis-Menten kinetics, then it is valid to define a KM and this equates to the substrate concentration when reaction velocity is 0.5 * Vmax. However, many enzymes do not exhibit Michaelis-Menten kinetics. One example is when the enzyme shows a co-operative response to ...


2

In terms of Michaelis-Menten kinetics, the rate never reaches the maximum rate: $v = V_{max} \times \frac{S}{K_m + S}$ where $S$ is substrate concentration. Notice that however large $S$ is, the term on the bottom line ($K_m + S$) will be larger than $S$, so $v$ will be less than $V_{max}$. You can think about this in terms of the binding equilibrium ...


2

As Arthur Kornberg said: "Don't waste clean thinking on dirty enzymes." Discovering an assay for a biological event in a cell-free extract opens the way to its molecular resolution and reconstitution (Commandment I). Trying to devise a mechanism with a crude extract, even with ingenious experiments, is generally a waste of effort. An extract is too ...


1

I'm going to try to lay out some basic definitions here in as plain language as I can find. Its difficult to study enzymes when they are outside the cell, where they may behave quite differently in different contexts. We categorize a given enzyme in its class by kcat, Km and by mechanism (the sort of reaction they catalyze. kcat is sort of a maximum ...


1

Alan Boyd's answer covers the mechanistic aspects quite well, but there is another aspect he didn't quite touch on - what's going on at the molecular level. To understand this, you need to think about the actual conditions of the reaction: unless it's taking place inside a cell, which straight biochemical reactions of the kind you're talking about almost ...


1

The answer is no really, but some variants might allow you to study inhibition. Michaelis Menten kinetics are experiments which try to characterize the catalysis characteristics of a reaction but to do so the numbers are obtained at concentrations of substrate that you dont find in a cell. Vmax is defined as the maximum rate at which the reaction is run ...



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