Questions tagged [proteins]

For questions about proteins. Proteins are biopolymers consisting primarily of polycondensated amino acids.

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17 views

How can I estimate the protein yield after purification?

I have a big problem. I have purified a protein and reached a nice purity ~90%, but now I would like to estimate the yield after each step as well. I have data from SDS-PAGE with lanes from the ...
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2answers
50 views

Can I normalize my data in order to compare it?

I have three chromatograms of the same eluted protein but at different concentrations, since it got diluted during purification process) and hence peak maximums at very different absorbances. The ...
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1answer
26 views

How should I interpret and present my total protein amount? [closed]

I have a problem. I have purified a protein with method A and then B. After method A I have a protein concentration of 20 mg/ml and after method B a concentration of 18 mg/ml. Method B is dialysis and ...
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1answer
38 views

How to pool fractions after chromatography?

I used chromatography to purify my protein and now I have fractions with different concentrations ranging from 1-16 mg/ml. Should I pool all these fractions or just the ones with high concentration (...
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16 views

Choice of buffer pH to avoid aggregation

I want to purify IgG which has a theoretical pI of 6.4-9.0 with an anion exchange column. I also want to keep the pH of my buffers as low as possible and "outside" the range of the pI to prevent ...
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1answer
13 views

How do I calculate the correct sample concentration for my measurements?

I will measure absorbance for measurement of protein concentration. The sample solutions are prepare in serial dilutions to the volume of 100 uL to obtain a certain concentration of the protein in ...
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13 views

Do I have to take the sample buffer into account when determining the protein concentration?

I am measuring the absorbance of a protein that is dissolved in a certain buffer. I know the extinction coefficient for this protein in this buffer. In order to be in the good absorbance range I have ...
4
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1answer
73 views

Can a protein complex be a machine? [closed]

Discussing an article with friends we began discussing whether a protein complex that punches holes in cells (membrane attack complex) would be considered a machine. Now, my friends are biochemistry ...
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21 views

Purifying cysteine containing peptides

I would like to purify my peptide having cysteine residue by using HPLC. It is known that thiol containing peptides undergo oxidation and form disulfide linkages. In order to prevent it I used proper ...
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16 views

Correct Generalization for Adair Equation?

I know how to derive the Adair Equation for n binding sites the long way, writing n+1 mini equations and linking them to relate all sub $K_b$ values to $K_{b-intrinsic}$. Tried to find a general ...
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3answers
71 views

What is the precise definition of Ramachandran angles?

The Wikipedia article Ramachandran plot is very schematic and doesn't even say when these angles are considered to be zero. It seems to assume that the peptide chain has no end, and always shows the ...
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1answer
30 views

Chemical Equilibria - Fraction Bound equation based on Kd, [R], [L], [RL], is actually an average?

Let's say 150 stem cells express exactly 150 copies of the same mebrane antigen X. While all differentiated cells express exactly 15 copies of X. To the cell mixture you add a large amount of 0.2 μM ...
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27 views

Which Flocculant/Coagulant is ideal for harvesting Algae?

While dealing with Algae fit for human consumption (as protein supplements), which is the most suitable coagulant/Flocculant available? Factors to consider: 1) Cost Effectiveness (for instance poly ...
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1answer
73 views

Why is casein hydrophobic?

According to this source hydrophobic behaviour occurs when a molecule does not have a charge or is neutral and therefore cannot be attracted to the negative nor positive parts of water. Casein has an ...
3
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1answer
73 views

Can glucose and insulin exist in the same container without reacting?

Someone asked if glucose and insulin could be mixed in the same container and used as an injection to provide a quick energy boost. I'm not interested about the medical part of this question, but just ...
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40 views

Developing a lab to identify the concentration of casein in organic milk

I am currently attempting to create a feasible lab design that will enable me to identify the concentration of casein protein in organic milk without having to use spectroscopy. Thus far I have ...
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1answer
151 views

Can =NH2+ in Arginine's side chain form hydrogen bonding at physiological pH?

I know that at physiological pH, Arginine will have its $\ce{=NH}$ protonated to $\ce{=NH2+}$. I was wondering if this $\ce{=NH2+}$ can still form a hydrogen bond by being a donor? And does the ...
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25 views

Molecular dynamics after modeling a protein loop. Necessary?

Firstly, I am postign this question to both chemistry and physics stacks exchange as I am not sure to which it belongs and to use the benefits from both sites. I have modeled missing loops in a PDB ...
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32 views

cluster of milk [closed]

I have a problem with milk when we are making yogurt in factory. When the milk pass through the machine it clogs the filter of the machine because the cluster that formed on the filter. My question is ...
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1answer
495 views

Is chitin actually protein?

Recently insects are featured as a protein rich source for human nutrition. That humans can really digest chitin through chitinase enzym has been only recently confirmed. But, does the chitin shell ...
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1answer
54 views

Why Greek yogurt has higher protein concentration?

During fermentation, no nitrogen is added and the number of amino acid molecules cannot increase. Why does it have a higher protein concentration than milk?
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1answer
277 views

Formating chemical equations for proteins binding in hugely complex configurations

In a previous question I asked about a simple case, I'm now trying to write equations for proteins that bind multivalently. In the simplest case proteins $A_1$ and $A_2$ can bind to up to two $L$ ...
3
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2answers
48 views

Why does the isoelectric range decrease as an Alanine chain grows longer?

The pK1 and 2 values for alanine are 2.3 and 9.7. In the dipeptide Ala-Ala, they are 3.1 and 8.3 and in tri-peptide Ala-Ala-Ala, they are 3.3 and 8.0. Why does this trend in pKa values exist? Why does ...
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1answer
283 views

How to dock aggregated structures comprised of “elementary” protein units like LEGO pieces?

There are proteins with intrinsic symmetries. For example: I was wondering how to use transformations such as: rotations, translation, replications to construct possible structures using 2 types of ...
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1answer
72 views

How to unify all the subunits in a PDB file?

A PDB may contain a TER token. For example, hemoglobin has 4 subunits separated by a TER identifier. If we take hemoglobin's ...
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1answer
205 views

How to write an entire trajectory into a single PDB file?

I have a trajectory (few frames) that I want to stack together and build a single PDB. I thought either to use VMD or MDAnalysis library. With VMD if I do ...
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1answer
189 views

How to visualize a crystal from a unit cell PDB and how to draw the unit cell's axes? [closed]

I am looking at the following PDB experimental data: Length (Å) Angle (°) a = 155.72 α = 90.00 b = 155.72 β = 90.00 c = 106.16 γ = 120.00 I find it hard to ...
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1answer
94 views

Biomolecular energy functions and entropy

From what I've been reading, it seems that entropy (rather than enthalpy) is the biggest driver of protein folding (especially the burying of hydrophobic residues). However, popular energy functions ...
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1answer
3k views

What happens to the t-butyl cation in the TFA deprotection of a t-butyl ester?

I am a first-year chemistry graduate student and I am currently learning how to synthesize proteins. I have reached a stage in the process where I need to deprotect a carboxylic acid moiety protected ...
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0answers
76 views

Calcium concentration in NMDARs e Nitric Oxide Synthase

My question is related to calcium $\ce{Ca^{2+}}$ concentration in NMDA receptors and nitric oxide synthase. I've found a very simple model that describes how the time change of calcium can be related ...
2
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1answer
410 views

What is the difference in the effect of DTT (Dithiotreitol) and SDS (sodium dodecyl sulfate) for PAGE?

In class, we have studied that when running a polyacrylamide gel with our protein sample to separate the proteins by molecular size, we can use several techniques, among which we have denaturing PAGE ...
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1answer
74 views

How to read these graphs and what are they called?

How does one interpret/read the following graph (found here) as well as on wikipedia or What are these called?
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57 views

Formating chemical equations for proteins binding in multiple configurations

I am working on problems involving protein-protein binding, particularly ones in which two proteins may bind in two or more configurations, and where some of the resultant structures may also bind ...
4
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1answer
325 views

Mono-oxidized and dioxidized tryptophan

I'm translating a Russian text in which there is the following diagram of tryptophan degradation: Further on in the text, hydroxytryptophan is called "the mono-oxidized form" (моноокисленная ...
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2answers
509 views

Why aren't chaperones considered to be catalysts?

I'm reading about protein folding on Wikipedia and I stumbled on a bit about a class of proteins called chaperones that aid in the folding of proteins by: ...reducing possible unwanted aggregations ...
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1answer
2k views

What is the nature of the Fe–O2 binding in oxymyoglobin and oxyhemoglobin?

Deoxymyoglobin ($\ce{Mb}$) is known to have iron in the +2 oxidation state; I believe this was deduced from its magnetic moment, which corresponds to four unpaired electrons in high-spin $\mathrm{d^6}$...
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1answer
658 views

Is protein folding thermodynamically favourable? If yes.. why? [duplicate]

The second law of thermodynamics dictates that the sum of entropy of the universe is always increasing. Is the process of protein folding a spontaneous process which is increasing the entropy? Is this ...
4
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1answer
201 views

How to measure a distance along the surface of a protein in a PDB

I would like to measure the distance between two active sites in a protein complex (pdb), but I do not find a straightforward way to do it. To be more precise I need the distance along the surface ...
4
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1answer
662 views

Using baking soda paste (alkaline) to “neutralize” honeybee venom (acidic). Is this scientifically sound?

I recall reading (courtesy: my 9th grade Chemistry text-book, chapter Acids, Bases and Salts), something along the lines of: Bee venom is acidic. This is why the area of skin (stung by a bee) is ...
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2answers
153 views

Why is the E2 protein important for protein degradation?

In the ubiquitination process, the E2 protein transfers ubiquitin from E1 to E3. Why can't E1 work with E3 directly to tag some protein with ubiquitin? Going further, why can't one of the E(1-3) ...
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1answer
138 views

Positive charge on a zwitter ion at pH=7?

I faced this question. But I am having some problems understanding the solution to this: How can the negative charge on the peptide vanish on $\pu{pH = 7}$? Suppose, we have some $\ce{H+}$ donor on ...
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97 views

How to make a sephadex slurry

I want to purify crude alpha-amylase with column chromatography. I am using a spehadex 75, But for some reason I can't find any information on how to make the slurry. I can quickly find tons of ...
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1answer
83 views

Collagen: similarity of human to fish and meat amino acids [closed]

I am looking for a collagen supplement for my partner who has joint pain, bone pain, fatigue associated with ligaments, flaccid skin problems, and is just over 40. As she does not eat fish or meat, ...
2
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367 views

proteolysis - how to determine the partial or completeness of the cleavage reaction?

Though the question is about biomolecules, we agree the underlying functions, formation, degradation etc come down to chemistry, (then physics and maths). I am posting it here to receive an ...
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75 views

Do proteins have a smell?

Proteins are heavy and not so volatile. Does it mean that pure proteins do not have a smell?
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3answers
889 views

Is it known for sure that bases feel slippery because of the production of soap/surfactant?

Discussion around the question Why does bleach feel slippery? has started me thinking about the saponification explanation for the slippery feeling of basic solutions. According to Wikipedia: ...
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0answers
35 views

Antiprion effectiveness of phenol

I am investigating ways to reliably decontaminate instrumentation that has come into contact with mammalian prions. Chaotropic salts and extreme pH are good at inactivating prions by disaggregating ...
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1k views

Terminology: what's the difference between “monomer” and “protomer”?

Using definitions from Wikipedia, a protomer is defined as "the structural unit of an oligomeric protein. It is the smallest unit composed of at least two different protein chains that form a larger ...
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1answer
661 views

Using electronegativity and atomic size to compare acidity of cysteine with serine

In proteins, the alcohol group of serine is generally more difficult to deprotonate than the thiol group of cysteine. Serine and cysteine respectively: In the literature, the explanation given is ...
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1answer
5k views

Why is % yield in a purification table measured using activity instead of total protein?

I'm trying to understand why % yield is measured with activity instead of total protein in mg. According to my biochemistry notes, activity is "1.0 units of enzyme activity = 1.0 μmol of substrate ...