Is it a valid generalization that kinases catalyse reactions involving energy transfer and utilization?

Question

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?

Answer 1

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.

Answer 2

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.