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Working principle of enzymes


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#1 lyok

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Posted 18 February 2012 - 10:06 AM

Hallo,
I havent had a lot of courses in biochemistry/enzymekinetics and I am struggling with a few things about enzymes.

For example on the wikipedia article about enzymes they mentions the following: "Enzymes catalyze the forward and backward reactions equally." What does this mean?
(link: http://en.wikipedia.org/wiki/Enzyme)

I checked it and I (seem) to understand the example (carbonic anhydrase, should catalyse both reactions), but does it mean that every enzyme catalyses both the forward and backward reactions? Or not all enzymes?

I am getting a bit confused because I learned that often: A => B (done by enzyme X) while B => A is done by another enzyme.

So does it just depend on the specific reaction?
Or?

And what with for example this: http://en.wikipedia....:Glycolysis.svg , you see some <=> in the shedule, does a <=> mean that both => and <= are catalysed by the same enzyme? Or does it mean that an enzyme can catalyse => and that <= can happen spontanously? (or maybe that both => and <= are catalysed by the same enzyme?)


Thanks in advance.

#2 phage434

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Posted 18 February 2012 - 12:21 PM

Enzymes (and catalysis in general) can only make reactions which would happen anyway happen faster, often dramatically faster. Every reaction is reversible, in principle. But reality can intrude. Cells may have very high concentrations of reactant A and little of B, so that the reaction A->B occurs preferentially. Some reaction products can be removed (i.e. it is a gas, or precipitates, or is the substrate for a subsequent reaction) making the reverse reaction rare. You need to understand equilibria and the role of concentrations in driving the equilibrium of reactions.

#3 ericacoleman

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Posted 18 February 2012 - 02:32 PM

On the subject of enzymes, I actually (although I do have a degree in Veterinary Medicine and Surgery) came upon this site in search of an answer to a very smelly problem. Someone last year was trying to isolate allinase from garlic. I have a real intolerance to Alliums and it is making life difficult. Has anyone gotten any further with isolating that enzyme. If not, can someone please do so! Evidently at least 3% of the population has onion intolerances, so we are looking at something that is properly commercially viable! A user named 'Ikwana' posted a question about the methods he would need to do so for his final year project a year ago. Any success guys?

The Gassy Vet

#4 bob1

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Posted 18 February 2012 - 04:38 PM

The gas produced by digesting onions and other alliums is usually from the breakdown of fructo-oligosaccharides (often referred to as FOS) by bacteria in the gut, garlic which doesn't seem to cause a lot of the problems doesn't contain much fos and is usually consumed in small amounts anyway, which may be why many people don't have as much of a problem with garlic. I am not sure that alliinase would be the magic bullet, it could well be that the intolerance you are experiencing is actually due to the allicin rather than the precursor alliin (I don't really have any idea - I'm not an immunologist).

From a quick search, it seems that the problem with alliinase is that the protein produced by the gene is further processed by some (perhaps unknown) mechanism, that makes it unviable to just produce it from cloned genes. I don't know it there is likely to be any easy/cheap way of extracting it in bulk from garlic or onions.

If you follow some of the links in the tables on the right hand side of the wikipedia page for alliinase, there are some papers on there that should be more helpful in gaining knowledge about the problems than I can be.

#5 lyok

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Posted 19 February 2012 - 01:29 AM

Enzymes (and catalysis in general) can only make reactions which would happen anyway happen faster, often dramatically faster. Every reaction is reversible, in principle. But reality can intrude. Cells may have very high concentrations of reactant A and little of B, so that the reaction A->B occurs preferentially. Some reaction products can be removed (i.e. it is a gas, or precipitates, or is the substrate for a subsequent reaction) making the reverse reaction rare. You need to understand equilibria and the role of concentrations in driving the equilibrium of reactions.


I see.

The problem I had, was that often they only refer to an enzyme as being a catalyst for just 1 reaction.. and I only found a few enzymes where they mentioned that it can also catalyse the opposite reaction.
While I learned in the past that a catalyst (in theory) should catalyst both reactions...
So I got confused about it, especially since they also started to mention that for some "reversible" reactions 2 different kinds of enzymes were used to catalyse the forward/backwards reactions.

#6 mdfenko

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Posted 21 February 2012 - 12:05 PM

there is a very nice "introduction to enzymes" at the worthington biochem website:

worthington introduction to enzymes

i'm also attaching a pdf of the site in case you can't access it.

Attached Files


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genius does what it must
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