What is the significance of high enzyme Km in enzyme regulation?

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In summary, the conversation discusses the reported Km of an enzyme and its relevance to the regulation of enzyme activity. The speaker is interested in finding more information on the statement that enzymes often work at substrate concentrations below the Km. They also question the idea that low Km is always better for regulating substrate. Additional discussion focuses on the sensitivity of enzyme activity to changes in substrate concentration and how this relates to allosterically regulated enzymes. Overall, it is suggested that altering the Km can influence the regulation of enzyme activity.
  • #1
gravenewworld
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I'm reading a reference right now on an enzyme I'm interested in, and the reported Km for the enzyme is in the mM range, which is much higher than the typical concentration of the enzyme's substrate that is found in the cell. The reference mentions "Enzymes often work at substrate concentrations below the Km, because the regulation of the
enzyme activity is easier then."Can anyone expound on this further? What does it mean? Where can I find more information on this statement? I'm having a hard time understanding that statement since biochemistry is not my expertise. I thought low Km was always better for regulation of the substrate, but why does high Km of the enzyme make it easier to regulate the enzyme?
 
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  • #2
Consider the sensitivity of the enzyme activity to the concentration of substrate (i.e. dv/d, where v is the reaction rate). At which points is activity most sensitive to ? When is the enzyme least sensitive to changes in ?
 
  • #3
I an not sure that the statement by itself really means anything, but it is true that in some well known allosterically regulated enzymes an inhibitor or an activator work by changing the affinity, the 1/Km or, if the kinetics are non-Michaelian, we must say the S0.5 (the half-saturating substrate concentration) and not the Vmax so in that case you can see...
 

1. What is the significance of a high enzyme Km?

A high enzyme Km indicates that the enzyme has a low affinity for its substrate, meaning that a higher concentration of substrate is needed to reach half of the maximum reaction rate. This can indicate a weaker binding between the enzyme and substrate, and may require higher concentrations of substrate for the reaction to occur efficiently.

2. How does a high enzyme Km affect enzyme activity?

A high enzyme Km can decrease enzyme activity, as it requires a higher concentration of substrate to reach half of the maximum reaction rate. This means that the enzyme may not be as efficient in converting substrate to product.

3. What can cause a high enzyme Km?

A high enzyme Km can be caused by a variety of factors, such as mutations in the enzyme's active site, changes in pH or temperature, or the presence of inhibitors. It can also be a natural characteristic of the enzyme, as some enzymes have a naturally low affinity for their substrate.

4. Can a high enzyme Km be beneficial?

Yes, a high enzyme Km can be beneficial in certain situations. For example, enzymes with a high Km are useful in breaking down large quantities of a substrate, such as in the digestive system. Additionally, a high Km can also provide a wider range of substrate concentrations for the enzyme to function, making it more adaptable to changing conditions.

5. Is a high enzyme Km always a bad thing?

Not necessarily. While a high enzyme Km may decrease enzyme activity, it can also provide advantages in certain environments. For example, some enzymes with high Km values are better suited for functioning in high temperatures or extreme pH levels. Additionally, a high Km can also allow for more control over the reaction rate, as the enzyme is less sensitive to small changes in substrate concentration.

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