#michaelis-menten

[the-art-of-medicine]

Michaelis-Menten Kinetics: enzyme kinetics model

Binding interaction between the enzyme and the substrate

[collegeandknowledge]

1st order reaction is just S^-1

2nd order reaction is M^-1S^-1

Michaelis-Menten equation says V0 = Vm[S] / (Km + [S])

Km is measured in Molarity

Catalytic efficiency is Kcat ÷ Km

Perfect enzymes have the highest Kcat÷Km values

A big Km puts your line in Lineweaver-Burk plot closer to the origin

The lower the slope in Lineweaver-Burk, the higher the catalytic efficiency

The number of active sites filled is [substrate]÷(Km + [substrate])

[hartmd-blog]

What I'm learning at Med School: Michaelis-Menten Part II

Although there wasn't any raging excitement over my last post, a few of my nerdy friends did appreciate it and I do think this is a good way of getting things straight in my own head. Enjoy part 2! A double reciprocal plot (Lineweaver-Burke) is the best way to use the Michaelis-Menten equation. The equation becomes: 1/v0 = (Km/Vmax)1/[S] + 1/Vmax The double reciprocal plot is useful because it has the format of y = mx + b, an equation we should all be comfortable with. So the y-intercept (1/Vmax) tells you the Vmax of the enzyme, and the x-intercept (-1/Km) tells you the Km. Where this starts to get interesting is when you consider enzyme inhibition. If you have a **competitive** inhibitor, then you would expect that the Vmax would remain the same, because by supplying an infinite larger amount of substrate you can out-compete the inhibitor and achieve the same Vmax. The Km on the other hand is going to decrease (since it basically describes the binding power of enzyme to substrate). The next class of inhibition is **noncompetitive**. This class of inhibitor acts at a place other than the active site. A noncompetitive inhibitor does not affect substrate binding which means Km stays the same. But its presence does reduce the amount of effective enzyme present. You cannot "out-compete" it by adding more substrate. Consequently the Vmax is reduced. The last class of inhibitors we'll consider is **uncompetitive**. Uncompetitive inhibitors will only bind to the enzyme-substrate complex. To see their effect on Km, you can think of this in terms of Le Chatelier's principle. Inhibitor binding to the ES complex reduces the ES concentration in solution, thereby favoring the production of more ES. Or, you could say that the inhibitor prevents ES from dissociating, which we know is measured by the numerator of Km. So naturally Km decreases. Vmax will also go down for the same reason as in noncompetitive binding. And no, you should not expect the slope (Km/Vmax) to be the same with or without inhibition.

[hartmd-blog]

What I'm learning at Med School: Michaelis-Menten

So, this post is really just an alternative way of studying, so I apologize in advance if it's incredibly dull. It's not my fault, it's the material! But the material is actually really cool, so I guess that makes it your own fault if you don't appreciate this post! The Michaelis-Menten equation is: V0 = Vmax [S]/([S]+KM). And the Michaelis constant: KM = (k-1+k2)/k1 The Michaelis-Menten equation is one of those ideas most bio undergrads are exposed to but just stare at blankly. What does it mean? It's used to describe the rate of an enzyme catalyzed reaction. Using the MM equation, there are a couple things we can deduce. At infinitely high levels of [S] (substrate), the equation becomes: V0 = Vmax meaning that is when the rate is at a maximum. When [S] is low compared to KM, then the equation approximates: V0 = Vmax[S]/KM and the rate is directly proportional to the amount of substrate in solution. If [S] is equal to KM, then the rate is at half of it's maximum value: V0 = Vmax/2 What does KM actually mean? In short it's the strength of interaction between the enzyme and the substrate. The equation shows that its value is equal to the rate of dissociation of the enzyme-substrate complex divided by the rate of formation. The catalytic efficiency of an enzyme is the best way of describing its "horsepower." It's the frequency at which the enzyme and substrate have productive encounters. It's calculated by kcat/KM (kcat is equal to k2, or in other words the rate constant for the product-generating dissociation of the enzyme and substrate). A larger value means the enzyme is more efficient. All of these values can be visualized much better, however, using a double reciprocal plot. Who wants to see Michaelis-Menten Part II?