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The Wikipedia entry for kinase states that "a kinase is an enzyme that catalyzes the transfer of phosphate groups from high-energy, phosphate-donating molecules [such as ATP] to specific substrates".

ATP is the energy currency of the cell, so, would it be accurate to say that a kinase catlayses reactions involving energy transfer and utilization within a cell?

David
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DJG
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    I intuitively think of kinases as switches: they allow molecules to exist as either a or b, and one or both forms may be active. – CKM May 12 '17 at 04:33
  • Care to elaborate, maybe with an example or two? – DJG May 12 '17 at 04:41
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    @CMosychuk — please follow the instructions for comments and do not use them to answer questions. It breaks the SE model and encourages others to do likewise. – David May 12 '17 at 06:46
  • Does the Wikipedia page on kinases not answer your question? Can you expand on what actually is the doubt, since the Wiki page has examples with specific functions fulfilled by kinases. – stochastic13 May 12 '17 at 10:48
  • I have put in a quotation from Wikipedia (Google is not a source) for kinase, and modified your definition of ATP to make it more acceptable. Kinase is the name of a a class of enzymes that catalyse certain types of reactions. I assume you are familiar with enzymes. I am not sure, however, how one thinks "intuitively" about them. One can generalize about the sort of reaction they catalyse. Is that what you are asking? – David May 12 '17 at 17:20
  • @David I think the OP's meaning is best described in the last sentence. OP knows that ATP is a form of energy, and knows that kinases convert ATP to ADP while they transfer a phosphate group to another molecule. OP wants to know, then: is it correct to think about a kinase as an enzyme that delivers stored energy within a cell? In my opinion, a good answer would explain that OP's description sounds a little more like what many ATPases do: they are using the energy from ATP to do some energetically unfavorable work. But also explaining that kinases have different functions... – Bryan Krause May 12 '17 at 17:27
  • ...and that in some anabolic pathways, yes, kinases are helping to deliver stored energy in the form of phosphate groups onto 'building blocks' of other molecules. But when a kinase adds a phosphate to regulate the function of another molecule, I wouldn't really say that it is delivering energy, just that there is some energy cost to doing the business of flipping cellular light switches, and ATP is readily available as a source to do that. – Bryan Krause May 12 '17 at 17:28
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    @BryanKrause That sounds like an answer to me. – canadianer May 12 '17 at 18:01
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    Wanted to add, it is Phosphoryl group that it is transferring and not Phosphate. Wikipedia is not a very good source for learning. – Tyto alba May 12 '17 at 18:15
  • @Tytoalba Good point, although I'd add that many sources besides Wikipedia talk about "transfering a phosphate" as the outcome of phosphorylation (I paged through some google scholar results for search terms like "kinase phosphorylation review" and confirmed this). I think it's intended as a bit of a shorthand, because the outcome is a phosphate group on the target, but it could also be a misstatement. For the biology (besides the specifics of the biochemistry) it doesn't really matter. – Bryan Krause May 12 '17 at 19:49
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    @Tytoalba Also I mostly blame the chemists who decided a phosphate+phosphoryl group would be called a "diphosphate", etc. ;) – Bryan Krause May 12 '17 at 19:50
  • I prefer the other term Pyrophosphate. @BryanKrause Yes it is Anidosinediphosphate again. – Tyto alba May 12 '17 at 20:17
  • @Tytoalba I am familiar with the existence of the term "pyrophosphate" but I have never seen it used in a biological context or to name a biological molecule. This question from chemistry suggests that the "bisphosphate" terminology is becoming more common in biochemistry for ortho-phosphates, whereas "pyrophosphate" is really only used for the inorganic anion. However I don't expect "ADP" and "ATP" to change for quite some time, if ever. Alas. – Bryan Krause May 12 '17 at 22:04
  • I have rewritten the question to make it generally more useful (before I answer it). It is best not to have subjective titles — in general we are not interested in you particularly — and a statement that talks about an enzyme ”metabolizing energy“ clearly will not do. Even though you can talk about energy metabolism, this actually means the metabolic reactions in which molecules with the potential to transfer free energy are generated. This may seem high-handed, but SE encourages improvement of both questions and answers. – David May 14 '17 at 13:29

2 Answers2

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Your (original) description:

a kinase helps chemically deliver or metabolize stored energy within a cell

sounds a little more like what many ATPases do: they are using the energy from ATP to do some energetically unfavorable work, such as moving molecules or ions against their concentration gradients. However, kinases have a broad range of different functions.

In some anabolic pathways, yes, kinases are helping to deliver stored energy in the form of phosphate groups onto 'building blocks' of other molecules, and this stored energy can be used for future reactions.

However, when a kinase phosphorylates another molecule (often a protein) to regulate its function, I wouldn't really say that it is delivering energy, just that there is some energy cost to doing the business of flipping cellular light switches, and ATP is readily available as a source to do that. One big advantage of using kinases in these sorts of reactions is that, because a fairly large energy input is required, such reactions don't occur easily by mistake or just due to thermal energy.

David
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Bryan Krause
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No.

  • It is not possible to suggest a verbal or pictorial generalization of the role of kinases.
  • It is futile to try to do so as it is incorrect to think that kinases have a single general role of the type suggested, or that the utilization of free energy from ATP is limited to reactions catalysed by kinases.

Clarification

Kinase is a surviving trivial name for enzymes that have been classified by IUBMB as ATP phosophotransferases. The categorization solely reflects aspects the chemistry of the reaction catalysed, and the sub-categorization in terms of substrate relects a diversity of roles. Moreover such kinase reactions are only one way in which the free energy of hydrolysis of the phosopho-diester bond of ATP can be utilized — transfer of the phosphoryl group to another molecule. Other types of reaction (and enzyme) are just as, if not more, important.

The diversity of roles played by kinases

I list at random some examples of different types of kinase reactions:

  1. Hexokinase transfers phosphate from ATP to glucose. One purpose is to creaate a charged molecule, glucose 6-phosphate, that cannot go back across the cell membrane.
  2. Thymidine kinase converts thymidine to TMP. Like several other kinases it can be thought of as catalysing a synthetic reaction, the phosphate being a part of the structure of the TMP (and ultimately TPP) molecules.
  3. Protein kinases transfer phosphate to serine, threonine or tyrosine residues of proteins. This is not using ATP for an energetic process, but to cause a change in the structure of the target protein that modulates its activity.
  4. Creatine kinase interconverts creatine and ATP with creatine phosphate (a rapidly mobilizable energy store in muscle) and ADP. As the reaction is reversible it can be thought as either catalysing the formation of creatine phosphate or its mobilization.
  5. Pyruvate kinase is a similar to 4 in that it produces ATP, and as the reaction it catalyses is essentially irreversible in the cell, the name is quite misleading about its function.

Non-kinase enzymes involved in utilizing ATP

These include ATPases, as @BryanKrause remarks, but also some others. Again, some examples at random:

  1. Sodium /Potassium ATPase catalyses active cation transport.
  2. Firefly luciferase (an oxidase) hydroyses ATP to produce light.
  3. Glutamine sythetase (glutamate-ammonia ligase) uses the free-energy of hydrolysis of ATP to convert glutamate and ammonia to glutamine.
David
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