For most receptors there exist different ligands that induce different responses. Depending on the response these different ligands can be classified into different groups such as agonists, antagonists, inverse antagonist, etc.

My question: is there a term that summarizes all of these different concepts?

I'm looking to express something like the following: 'addition of a methyl group to the phenyl ring changed its X from agonist to antagonist.'


2 Answers 2



"addition of a methyl group to the phenyl ring changed its activity from agonist to antagonist"


A technical word that encompasses agonists, antagonists etc. is effector, defined in the Wikipedia entry as follows:


In biochemistry, an effector molecule is usually a small molecule that selectively binds to a protein and regulates its biological activity.

However ‘effector’ does tend to be used more in regulation of enzyme activity than signal transduction. I suggest this is preferable to the term ‘activity’, suggested by @DeNovo as it is the targets of agonists etc. that exhibit the biological activity that one may be considering, rather than the agonists themselves. Such effectors modulate the activity of other molecules, so one could even consider using the term ‘modulator’, described in a Wikipedia entry — for the particular case of allostery — as follows:

Allosteric Modulator

In biochemistry and pharmacology, an allosteric modulator (allo- from the Greek meaning "other") is a substance which indirectly influences (modulates) the effects of a primary ligand that directly activates or deactivates the function of a target protein.

However I would definitely not use a noun of this sort to convey the idea of your sentence.

I find that more complex and clumsy then necessary. Far better, in my opinion, to express yourself in simpler terms and more directly.

“Addition of a methyl group to the phenyl ring changed it from being an agonist to an antagonist.”


“Addition of a methyl group to the phenyl ring changed its action from that of an agonist to that of an antagonist.”

However ‘effector’ might be useful as a portmanteau description of agonists etc. in circumstances when you are listing things.

  • 1
    $\begingroup$ "Portmanteau - A word formed by merging the sounds and meanings of two different words" - American Heritage Dict.; "A word blending the sounds and combining the meanings of two others, for example motel (from ‘motor’ and ‘hotel’)" - Oxford Living Dictionaries $\endgroup$
    – mgkrebbs
    Aug 20, 2018 at 17:25
  • $\begingroup$ @mgkrebbs — Umbrellas at dawn! I referred to a portmanteau 'description'' not a 'word'. I use British English Dictionaries that include the definition in the sense I used it (and have used it all my life). Thus, Chambers on my iPhone has "Adjective: Combining or covering two or more things of the same kind". And Cambridge has the example "The Official Secrets Act was described as a piece of portmanteau legislation, covering everything from nuclear weapons to army boots" and also has an example with the word "motivation". $\endgroup$
    – David
    Aug 20, 2018 at 21:17

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