14
votes
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Is it possible to make an anticatalyst?
Some substances do exist that slow down reactions and they're different from catalytic inhibitors/poisons. Such substances are called negative catalysts. Here is one example I can think of right now:
$...
- 4,016
13
votes
What is an example of chemical reaction that can be assisted by both an inorganic catalyst and an enzyme?
A good example is the conversion of hydrogen peroxide to oxygen and water
$$\ce{2H2O2 ->2H2O + O2}$$
It can be catalyzed by catalase, which has one of the highest known turnover numbers, or by an ...
- 18.9k
11
votes
What is an example of chemical reaction that can be assisted by both an inorganic catalyst and an enzyme?
There are many many examples of reactions that are usually done in biological systems with an enzyme, but can be done outside in the lab with general acid or base catalysis.
Take for example the ...
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9
votes
Accepted
Why is the units of kcat 1/s?
The turnover frequency is a rate. (It's actually the kinetic rate of the reaction in saturating substrate concentration, normalized to the amount of enzyme.)
It might be helpful to think about ...
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9
votes
Accepted
How do I eliminate the disagreeable odor of soy milk?
A few things first:
Enzymes are proteins (usually) that promote or accelerate a biochemical reaction. The enzyme lipoxygenase in particular, promotes the dioxygenation of some lipids called ...
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8
votes
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How does fluorouracil inhibit thymidylate synthase?
The inhibition comes about because:
Uracil and $5$-fluorouracil are sufficiently similar that both moieties have a strong binding affinity for the active site of thymidylate synthase.
The presence of ...
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8
votes
Why do so many biochemical reactions require enzymes?
all 10 steps in glycolysis require an enzyme
We count it as 10 steps because there are 10 enzymes. There might be other steps that are fast (like a product acting as an acid or base) that we don't ...
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7
votes
Accepted
When an enzyme is diluted with water, what is slowing down the rate of reaction?
[…] there's the same number of catalase molecule within an undiluted and a diluted solution. Also, seeing as water is not an enzyme inhibitor, […]
Q: Why is dating between a fixed ...
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7
votes
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How does a hydrophobic environment help in bond formation?
The major reason of the ‘hydrophobic environment’ is to block the enzyme-complex from accessing the solvent (water), which might otherwise enter the active site and hydrolyse ATP.
The reduction of ...
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7
votes
What is an example of chemical reaction that can be assisted by both an inorganic catalyst and an enzyme?
Sucrose inversion (hydrolysis of sucrose into fructose and glucose).
Done with invertase — that's how human body breaks it down and that's how bees make honey.
Done with any acid at elevated ...
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6
votes
Accepted
Why does the Michaelis-Menten constant remain constant in the event of non-competitive enzyme inhibition?
This is a question that is relatively easy to answer mathematically.
To keep the algebra a little simpler, let me use a simplified Michaelis-Menten mechanism, where we assume that the enzyme-...
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6
votes
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Why is fermentation of cellulose to produce biofuel and nutrients so difficult?
Your question is a little bit all over the place, but I believe I can answer it anyway. First, though, allow me to point out that your sum formula for cellulose is wrong. While glucose is indeed a ...
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6
votes
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Is chitin actually protein?
Chitin and protein are completely unrelated.
The only common thing is that they are polymers.
Chitin is a polymer of amino sugars while protein is a polymer of amino acids.
Both monomers are very ...
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6
votes
Why do so many biochemical reactions require enzymes?
Enzymes act as catalysts to increase the rate of reactions. In the absence of enzymes, most biological reactions would be incredibly slow, in some cases many many orders of magnitude slower than when ...
- 9,107
6
votes
Why use Km in catalytic efficiency?
The most basic kinetic scheme for enzymes is represented as
$$\ce{E + S <=>[K_m] ES ->[k_{cat}] E + P}$$
As should be clear, the $k_{cat}$ is the rate constant for the reaction that occurs ...
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6
votes
Why use Km in catalytic efficiency?
The turnover number or catalytic constant $ k_{\mathrm{cat}}$ in the Michaelis-Menten model is the rate constant for the productive dissociation of intermediate $\ce{ES}$:
$$\nu = k_{\mathrm{cat}}[\ce{...
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6
votes
Accepted
How does coenzyme A produce proton from pyruvate ions?
The reversible conversion of pyruvate ion and coenzyme A (CoA) into $\ce{acetyl-CoA}$ and formate ion (Figure 1) is not a one step reaction but a complex multistep radical reaction (Ref.1), thus it is ...
- 35.4k
5
votes
Can a very high concentration of hydrogen peroxide, inhibit or denature the enzyme catalase?
20% hydrogen peroxide sounds HUGE. But something can happen that is called substrate inhibition. It can be detected if the substrate acts as a non-competitive reversible inhibitor (i.e. binds only to ...
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5
votes
Is dextrose an isomer of glucose?
There are two enantiomeric forms of glucose, D- and L, with D-glucose being the naturally occurring form. Dextrose is just another common name for D-glucose, so if a microorganism can metabolise D-...
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5
votes
Phosphoglucose isomerase mechanism
tl;dr: The active site catalytic residues (BH+ and B’) are thought to be Lys and a His–Glu dyad, respectively. These facilitate the abstraction of proton from C2 and subsequent protonation on C-1.
...
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5
votes
Accepted
Derivation of an equality in Michaelis–Menten kinetics
Your equation
$$\ce{Enzyme + Substrate <=>[k_1] ES complex ->[k_2] Enzyme + Product}$$
contains only two rate constants, $k_1$ and $k_2$, but not $k_{cat}$ you refer to.
The correct ...
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5
votes
Why is fermentation of cellulose to produce biofuel and nutrients so difficult?
The ultimate reason is that cellulose is designed to be hard to digest
The specific chemical reason is well covered in Jan's answer, but there is an explanation that is simpler and more fundamental: ...
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5
votes
Accepted
What is the fate of sulfur in cysteine when it participates in gluconeogenesis?
Cysteine is a dispensable amino acid required for synthesis of protein and non-protein compounds. These non-protein compounds include pyruate (hence acetyl coenzyme A), taurine, sulfate, and ...
- 35.4k
5
votes
Representation of bromelain molecule in two dimensional diagram
I think I got it. The diagram in PubChem is not bromelain molecule, but a tiny fragment of it. This thing is indeed too small to be an enzyme. Also, it has nothing to do with proteins. Look at the ...
- 30k
5
votes
Accepted
What is a secondary shell in an enzyme?
The authors mention three residues that they consider "second shell", 12, 77, and 102. They are shown in the figure below in green:
Residues Trp50 and Glu101 are directly involved in ligand binding, ...
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5
votes
Why do so many biochemical reactions require enzymes?
We speak of reactions that
build complex molecules
or break complex molecules at a specific position
they must happen at constant 37°C
all of which must be rather low energy
or be very well ...
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5
votes
What is an example of chemical reaction that can be assisted by both an inorganic catalyst and an enzyme?
Fixing Nitrogen
What "fixing" nitrogen means it taking the–very unreactive–dinitrogen molecule which is the major component of air and turning it into something that is more reactive and can ...
- 32.6k
4
votes
Accepted
Rate constant and Michaelis Menten
Given $\ce{E + S <=>ES -> E + P}$
$\frac{d[\ce{ES}]}{dt}=-\frac{d[\ce{E}]}{dt}= k_1[\ce{E}][\ce{S}]-k_2[\ce{ES}] -k_3[\ce{ES}] $
is the slope of $[ES]$ equal to $k_2$ ?
no
is the ...
- 39k
4
votes
Enzyme Specificity vs Selectivity
Specificity is the term used to define the selectivity of enzymes
for their substrates. The selective qualities of an enzyme are collectively recognized as its specificity.
Other texts have ...
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