In biochemistry, Michaelis–Menten kinetics is one of the best-known models of enzyme kinetics. It is named after German biochemistLeonor Michaelis and Canadian physician Maud Menten. The model takes the form of an equation describing the rate of enzymatic reactions, by relating reaction rate to , the concentration of a substrate S. Its formula is given by
.
Dear Dr. Mahmoud If you trace the definition of Michaelis–Menten constant (is the substrate concentration at which the reaction rate is half of Vmax) you need to calculate Km for all substrates participate in the reaction individually. So, I think in such reaction Km is not represented value.
Is this a homework question? Do you mean that...
- you do not get the typical curve (don't reach saturation, sigmoidal, etc)
- you know that you are not fulfilling the theoretical constraints necessary to derive the michaelis menten equation
- you are not in the proper kinetic regime (i.e. one component in vast excess is being titrated, the other component in trace is significantly below the Km/Kd)
Real problems can be more scary than perused equations. I got the sane problem long ago. We isolated a nemonic-enzyme but the results did not fit the M-M, the person in charge suggest us to look for enzymes with memory. Precisely that was the case, we solved the mystery right away following the kinetic before we tried the usual substrate saturation. Do you have a two substrate enzyme? You need to know how much it takes to saturate E with either substrate.
Foe example A + B + Enzyme = ... = C + D + enzyme. Have fun, it is really.
A excellent book, for prepared readers is:
"Fundamentals of Enzyme Kinetics" Wiley–Blackwell, 4th edition of Athel Cornish-Bowden (2012) .
Sometimes enzymes have mechanistic quirks that can't be modeled using MM kinetcs. The solution is to make a model of the actual reaction. One of the enzymes I study (neural nitric oxide synthase) turns itself off after a few turnovers, and all enzymes I've seen with a P450 reductase type component show substrate inhibition at high NADPH concentrations. Substrate inhibition is a prime cause of non-MM behavior. The bad news is you have to think hard. The good news is the chance to publish a new model.
Dear Dr. Mahmoud If you trace the definition of Michaelis–Menten constant (is the substrate concentration at which the reaction rate is half of Vmax) you need to calculate Km for all substrates participate in the reaction individually. So, I think in such reaction Km is not represented value.
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