Questions tagged [enzyme-kinetics]

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7
votes
3answers
339 views

Why use Km in catalytic efficiency?

The catalytic efficiency of an enzyme is given by $k_{cat}/k_M$ where $k_{cat}$ is the turnover number, or the number of molecules that can be produced per second per active site of an enzyme. $K_{M}$ ...
7
votes
1answer
92 views

How can subtilisin still function without its catalytic triad?

I read chapter 9 in the book Biochemistry (5th edition), by Berg, Tymoczko, and Stryer (provided in the NCBI site here). It describes the mechanism of action of the chymotrypsin enzyme. The catalysis ...
6
votes
2answers
294 views

What is the fate of sulfur in cysteine when it participates in gluconeogenesis?

Amino acids can be broken down to yield pyruvate, which in turn can be used to construct glucose molecule in the process of gluconeogenesis. What happens to the sulfur atom in the amino acid cysteine ...
5
votes
1answer
135 views

Calculate Michaelis-Menten constant of enzyme catalyzed reaction

I have: $$\begin{array}{c|c} \dfrac{v }{ [S]}/\pu{s^{-1}} & v \cdot 10^2/\pu{mol dm^-3 s^-1} \\ \hline 0.257\ & 5.15\\ 0.895 & 4.48\\ 2.00\ & 3.35\\ 3.59\ & 1.8\\ 4.82\ & 0....
5
votes
1answer
100 views

How do enzymes affect a reaction's equilibrium?

I am not sure to understand something I read in a educational journal (1) Introduction Lets consider the following reversible enzyme-catalysed reversible reaction; $$E + S \leftrightharpoons ES \...
5
votes
1answer
542 views

Hill equation with inhibition and activation

The Hill equation for an activating enzymatic interaction with cooperative multiplicity $n$ is $$\frac{\mathrm d[\ce{P}]}{\mathrm dt} = V_\mathrm{max}\frac{[\ce{S}]^n}{K_\ce{S} + [\ce{S}]^n}\tag{1}$$ ...
4
votes
2answers
83 views

Determine vmax and enzyme concentration (Michaelis–Menten)

I am given that the enzyme concentration is $\pu{15 nM}$ and the following data: $$ \begin{array}{rl} \hline S/\pu{mM} & V/\pu{mM s^{-1}} \\ \hline 1 & 0.202 \\ 2 & 0.368 \\ 5 & 0....
4
votes
2answers
92 views

Measuring a high Michaelis constant using fluorescence

We have the task of measuring kinetic parameters of an oxidase reaction that has a $K_M$ of about $2 \,\text{mM}$. For that, we want to use a fluorescence assay based on Amplex Red. The latter is a ...
4
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3answers
136 views

Temperature dependence of reaction rates

Is it correct to say that "Increasing the temperature will always increase the rate of any chemical reaction"? Many articles on the internet and textbooks say yes but what about biochemical reactions ...
3
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1answer
93 views

Why a catalyst is not consumed in a reaction when all steps are reversible?

It is said that a catalyst speeds up the rate of a reaction but is not consumed (assuming no side reactions take place). Suppose we have the following reaction: $$\ce{A + B <=> C} $$ catalysed ...
3
votes
1answer
95 views

Michaelis-Menten rate law for enzyme which catalyzes two reactions: steady state?

Suppose an enzyme $\ce{E}$ can catalyze two reactions: \begin{align} \ce{S1 + E &<=> S1E -> P1 + E} \tag{R1} \\ \ce{S2 + E &<=> S2E -> P2 + E} \tag{R2} \end{align} I want ...
3
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1answer
106 views

Lowest Michaelis constant Km

I want to find a lower limit of the Michaelis constant for some evaluations of Michaelis-Menten enzyme kinetics. What is the lowest $K_m$ you ever encountered? Is there a theoretical limit?
3
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0answers
33 views

Why neglecting Bradford Solution Volume in the assay?

I would like to know why do we not need to take account of Bradford agent solution in dilution calculation? For example, $\pu{2.5 \mu g mL-1}$ BSA will calculate from $\pu{0.4 \mu L}$ of $\pu{1 mg mL-...
3
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0answers
28 views

Why does allosteric binding produce a sigmoidal curve?

Allosteric binding is where the enzyme can be regulated through having ligands bind onto somewhere that is not the active site. This will then induce a conformational change on the active site, hence ...
3
votes
0answers
64 views

Equations Used in Isothermal Titration Calorimetry

I have been attempting to understand and derive the formulas used for ITC which can be found here starting on page 310. I am particularly interested in the single set of identical sites. To first ...
2
votes
1answer
83 views

Michaelis menten constant motivation behind 1/2?

So the michaelis constant is defined as the substrate concentration at half maximal „reaction-speed“. I was wondering why 1/2 ? I guess for higher values you need more substrate, which could be a ...
2
votes
1answer
196 views

High concentration of ferric ion catalyst decreases rate of decomposition of hydrogen peroxide in the Fenton reaction

I did a project on the Fenton reaction and rate of decomposition of $\ce{H2O2}$. I used colorimetry to measure the rate of decolourisation of methylene blue when I mixed $\pu{5e-6 mol}$ $\ce{FeCl3}$ ...
2
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0answers
57 views

How to find the reaction rate in an enzyme reaction?

First time posting questions here, so let me know if I need to edit anything. I need to decide $dC/dt$ and $dP/dt$ when the reaction is like this, where I only know we must have 2 substrates $S$ to ...
2
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0answers
43 views

Solving for Concentration Using pseudo-First Order Kinetics

The following graphs represent a pseudo-first order bi-molecular reversible reaction with the formula $\ce{A + B <=> C}$: The reaction product has an extinction coefficient of $\pu{50000 M-1 cm-...
1
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1answer
241 views

Why enzyme-catalyzed reactions mostly go one way?

I listened to the lecture about enzymes. Professor downplayed the question in the subject. He said that enzymes are able to work both ways, but practically speaking reactions with overwhelming ...
1
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1answer
57 views

How to calculate the kinetic order of an enzymatic reaction?

This question is concerning the metabolism of ethanol by an alcohol dehydrogenase enzyme. Usually people metabolize alcohol equivalent to "one beer per hour". One beer is said to contain 33cL. The ...
1
vote
1answer
57 views

Enzyme Kinetics two enzymes in complex with one substrate

Given an enzyme reaction where two enzymes are required to form the complex, for example $\ce{2E +S-> E3S->2E +P}$, how would I calculate complex concentration assuming steady state ...
1
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1answer
82 views

Are enzymes with superior catalytic properties more sensitive to temperature changes?

I am wondering whether enzymes with superior catalytic properties are more or less temperature sensitive than average enzymes. I know that enzymes lower the activation energy, Ea. So the more ...
1
vote
2answers
48 views

Can you discriminate a monooxygenase from other enzymatic mechanisms by the requirement of NADPH?

I am working on a project about CYPs 450. It seems that most of them function as monooxygenases but there are other categories as well. Assuming that the question makes sense, is it correct to say ...
1
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0answers
20 views

Given the pH optimum of Angiotensin 1, how do I determine its charge?

I'm given the following information I'm then asked to determine the charge of the substrate Angiotensin 1 at the pH-optimum. I have found the pH-optimum to be 6.9. How do I go about answering this ...
0
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2answers
201 views

Enzyme Kinetics - Given Km find substrate concentration at a certain velocity

From what I understand about the Michaelis Menten Model Km defines the amount of substrate required to reach half-saturation. 1/2 Vmax corresponds to Km on the x axis Generic formula is v = Kcat [...
0
votes
1answer
205 views

How can some enzymes work faster than the diffusion rates of the reactants allow?

Quoting Wikipedia: "Some enzymes operate with kinetics which are faster than diffusion rates, which would seem to be impossible." Which are those enzymes and how can they be so fast? One example is ...
0
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1answer
42 views

Question on notation

Here, when they write $v/(\mathrm{mol\ s^{-1}\ (kg\ \text{protein})^{-1}})$ is $0.30$ for the first row first column, do they mean that the value is $0.30\ \mathrm{mol\ s^{-1}\ (kg\ \text{protein})^{-...
0
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1answer
66 views

Inactivation of enzyme: Why inactivation constants do not follow the Arrhenius equation? [closed]

The Arrhenius equation may not account for the temperature effect on thermal inactivation rate constants. Why can the thermal inactivation kinetics not be expected to follow Arrhenius? The reason that ...
-1
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1answer
22 views

Could shear force from blending denature alpha amylase / glucoamylase enzymes?

I am trying to break down the starches in a certain variety of oats in the most efficient way possible. I have to break the whole oats down after cooking, so they are finer particles for the amylases ...