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I understand that enzyme concentration does'nt affect Km since the Micaelis Menten equation is based on the steady state approximation wich requires high levels of substrate compared to enzyme (that's why changing enzyme concentration is negligible compared to substrate concentration and therfore there is no apparent change in Km). but what about change of temperature or pH? it's known that change in those parameters can change enzyme activity, but does this actually can change kinetic parameters like Km? Why should i think not? because the same explanation that says that change in enzyme concentration does'nt affect Km sould be applied here. there is a lot of substarate anyway and therefore there should not be apparent change in the Km? or am I wrong? another issue which makes me think so: In all the biochemistry literature that I have encounterd Km and Kcat appears for each enzyme with no indication of the temperature or pH for wich thouse values were observed (not in Leninger, nor Wikipedia or other textbooks).

I couldn't find any orderd explanation about this issue.

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    $\begingroup$ Wikipedia: “The value of Km is dependent on both the identity of enzyme and that of the substrate, as well as conditions such as temperature and pH.” $\endgroup$
    – acvill
    Jan 2, 2022 at 16:45

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Michaelis constant is defined as $$K_\textrm{M} = \frac{k_{-1}+k_2}{k_1},$$ where $k$s represent the rate constants for the reactions $$\mathrm{E+S} \;\;\underset{k_{-1}}{\overset{k_1}{\longrightleftharpoons}} \;\;\mathrm{ES}\; \overset{k_2}{\longrightarrow}\;\mathrm{E+P}.$$ Rate constants can generally be expressed by the Arrhenius equation: $$k(T) = A(T)\exp\left(-\frac{E_a}{RT}\right).$$ Because the parameters $A(T)$ (pre-exponential factor) and $E_a$ (activation energy) are generally not equal for all three reactions, the change in temperature does change the value of $K_\rm{M}$.

When measuring the enzyme kinetics and calculating $K_\rm{M}$, one has to explicitly state at which temperature the experiments were performed. This is probably not mentioned afterwards in the textbook because it is not of significant importance to the surrounding text and concepts.

Here you can find an article example with the measurements of enzyme kinetics at different temperatures. You can clearly see the change in $K_\rm{M}$.

Enzyme Kinetics

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