19
According to "Resolution of distinct rotational substeps by submillisecond kinetic analysis of F1-ATPase" (Yasuda et al., Nature, 2001), ATPase rotates at 130 revolutions per second when saturated with ATP.
19
It seems that yes, it is possible to increase the tolerance for lactose over time, and it has to do with the adaptation of microbiota.
A simplistic explanation comes in the following article:
Hertzler SR, Savaiano DA. 1996. Colonic adaptation to daily lactose feeding in lactose maldigesters reduces lactose intolerance. The American journal of clinical ...
16
Simple Answer: Nothing.
Background: First of all, I must tell that your statement So why doesn't pepsin acts on the milk proteins? is based on wrong assumption that pepsin does not act on milk proteins.
Milk contains a protein called casein, which has many different types (usually, we talk about $\kappa$-casein). Infants, which are dependent solely on milk ...
15
Enzymes alter the rate of a reaction by lowering activation energy; they have no effect on the reaction equilibrium ($\ce{K_{eq}}$). Since $\ce{K_{eq}=\frac{k_f}{k_r}}$ and $\ce{K_{eq}}$ is constant, an increase in forward rate ($\ce{k_f}$) requires a corresponding increase in the reverse rate ($\ce{k_r}$). Intuitively it may help to think that the same ...
14
The formation of protein complexes or aggregates in aqueous buffers is determined by a number of factors: physical properties of the protein itself, pH, temperature, type and concentration of the used cosolvent (salt). Solutes are often roughly divided by type into chaotropes ('disorder-making'), which destabilise protein structures and kosmotropes ('order-...
13
It's just so much more convenient to have the enzymes ready without having to thaw them. The main reason you freeze enzymes is to keep them active, if you figure out a buffer that keeps them unfrozen without compromising activity, that is a huge increase in convenience.
Not having to thaw the enzymes before use saves a lot of time, if you can manage to keep ...
13
Enzymes can catalyze a thermodynamically unfavorable reaction by coupling it with a thermodynamically favorable reaction. Most often, enzymes use ATP hydrolysis reaction (energetically favorable) as a source of energy (in simple terms) to drive the unfavorable reaction forward. One important point to keep in mind here is that enzymes don't drive a reaction ...
13
Can enzymes catalyze thermodynamically unfavourable reactions?
Enzymes don't change the equilibrium of a reaction, but the fact that an equilibrium exists means that the reaction proceeds in both the forward and reverse directions. Before equilibrium is attained, ΔG for the reaction is not 0. Thus, by definition, one direction is thermodynamically ...
11
No, not all enzymes (or other proteins for that matter) can be obtained in functional form by recombinant expression with today's methods. As you suspect, problems arise when complex post-translational modifications are necessary to obtain the correct function.
Direct modifications to peptide is one potential problem. Some of these can be resolved by ...
11
Short answer
The direction of rotation depends on the viewing point of the observer and the reaction catalyzed by the ATP synthase. When synthesizing ATP, and viewed 'from the bottom' (observer faces the intermembrane space looking into the mitochondrial matrix) it rotates clockwise.
Background
ATP synthase is a membrane bound enzyme with two large subunits;...
11
What about the ATP synthase? https://en.wikipedia.org/wiki/ATP_synthase it uses proton flow to generate ATP but it can also burn ATP to generate proton flow.
Like other enzymes, the activity of F1FO ATP synthase is reversible.
Large-enough quantities of ATP cause it to create a transmembrane
proton gradient, this is used by fermenting bacteria that do ...
10
Image from wikipedia page on ATP synthase
In brief, the addition and release of protons to the structure cause a conformational change that leads to another conformational change. This series of conformational changes occurs in such a way that it induces a rotational motion.
The rotation of the central axel that extends through both hemispheres of this ...
10
This terminology is at least as old as September 1944 when Enzymatic Synthesis of Acetyl Phosphate Journal of Biological Chemistry
155, 55-70 was published by Lipmann, which says:
Inorganic phosphate, referred to as Pi, was estimated
colorimetrically
See also the definition of "inorganic phosphate" and "orthophosphate" from this 1943 University of ...
9
This is true of all protein binding as well as the special case of enzyme-substrate interaction:
Various proteins are more dynamic than others: some have only one or two overall conformations and are relatively implastic otherwise. An example would be a receptor tyrosine kinase like Kit (or CD117, or Mast Stem Cell Growth Factor Receptor, whatever you want ...
9
You can certainly get massive differences between EC50 and affinity. This is especially true for cell-based assays and membrane protein systems.
The reason why is because the appropriate time scales to achieve binding equilibrium (hrs for nM affinity, days for picomolar, feptomolar affinity according to back of the envelope calculations) may be and likely ...
9
The macromolecule concentration within E Coli is estimated to be around 0.3-0.4 g/ml [1]
The concentrations of your substrate in respect to your enzyme are generally fairly analogous to in vitro studies compared to in vivo studies. However, this is heavily based on the assumption that the diffusion constants for both molecules stay consistent. In many cases ...
9
The answer given by Sadegh gives a general correct broad view. But one part of the puzzle is missing, which is molecular recognition.
Molecules bind to each other via physical/chemical interaction like forming hydrogen bonds, electrostatic interactions and other mechanisms. The sum of all interaction defines the strength of the binding. If molecules have ...
8
Composition of E. coli (dry weight): 55% protein, 20% RNA, 10% lipid, 15% other
Protein concentration is about 100 mg/ml or 3 mM. From the size of an E. coli cell, 1 nM is about 1 molecule/cell. This is ~1000 molecules/cell for HeLa cells.
Diffusion coefficient for an "average" protein: D ~ 5-15 microns^2/s, or ~10 ms to traverse an E. coli. For reference, ...
8
I think the KEGG pathway database may be of some use to you.
Link is here: http://www.genome.jp/kegg/pathway.html
This a database of manually drawn pathway maps, I have used the site myself and it is very useful in determining if your enzyme is in a pathway and where it lies in it. This is assuming though, your enzyme is in the database and has been ...
8
Yes, something can be both a hormone and an enzyme. There are a group of hormones known as peptide hormones. These are proteins (such as enzymes) that act as hormones indirectly (and maybe directly too?). A hormone is a chemical secreted by a cell that has some effect on another cell elsewhere in the body. In this case, the chemical just happens to be an ...
8
As @Chris commented, when assayed in vitro with a single substrate (which may not even be the physiological one) most enzymes can catalyse a reaction in either direction. And enzymes such as pyruvate kinase were discovered before the pathways they are constituents of were worked out in full. Furthermore, the ways of naming enzymes only became more ...
7
First of all we should distinguish between the physiological clotting factors that are parts of the normal clotting pathways, and those that might affect clotting pathways but are not observed under healthy conditions.
TPA (tissue plasminogen activation), PAI-1 (plasminogen activator inhibitor) and prothrombin are normal clotting factors that are essential ...
7
It is possible to search for enzymes or a series of enzymes that will take similar reactants to similar products.
ReBIT allows you to query enzymes by your molecular structures of interest using their SMILES code. Unfortunately, a quick search using coumarin didn't produce any results but searches for phenol and phenolate gave some hits.
If you're seeking ...
7
This refers to the turnover number (a.k.a kcat or k2) of an enzyme and is usually calculated using Michaelis-Menten kinetics. Jump to the summary at the end if you want a simple answer. If you want a more thorough answer, consider the following chemical equation:
[E] + [S] ⇌ [ES] → [E] + [P]
This says that a certain concentration of enzyme mixed with a ...
7
In what follows I am going to attempt to answer your question using a specific example of (competitive) reversible activation, and I hope to show what a misleading parameter EC50 can be. (Rate law derivation is an area of interest, hence the long-winded answer).
It can of course give information, but IMO it needs to be used with extreme care.
I am ...
7
How are diabetes and obesity connected in light of low lipase activity?
Short answer: There's more than one type of diabetes. (And to complicate things, there's also more than one type of lipase. It's unclear from the question which type were mentioned in what you read.)
Diabetes mellitus is usually divided into Type 1 (insulin-deficient) and Type 2 (...
7
The mechanism of aconitase classifies it as a lyase, even if (under most physiological conditions), the relative concentrations of substrates results in it catalysing the conversion of citrate to isocitrate. In short, it is not an isomerase because the substrate is released after each step.
As the mechanism of aconitase shows, it catalyses the conversion of ...
7
Examples of enzymes working in reverse?
Except three enzymes of Glycolysis (Hexokinase, PFK-I and Pyruvate kinase) all catalyse reversible reactions.
As these enzymes catalyse the backward reactions too they are part of Gluconeogenesis pathway.
(A comparison between the two pathways)
7
Until the late 1980's all enzymes* were believed to be proteins, and were often defined as protein catalysts, often in textbooks which are often not perfect representations of science. At that point every macromolecular biological catalyst known was a protein so they thought all macromolecular catalysts were proteins. But the discovery of ribozymes (RNA ...
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