Psycho-Babble Medication Thread 225362

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What does irreversible mean? (MAOI)

Posted by zarathustra on May 9, 2003, at 10:04:12

I take parnate 20mg B.I.D.

what does irreversible mean? Is it permanent?

Re: What does irreversible mean? (MAOI)

Posted by Larry Hoover on May 9, 2003, at 10:59:40

In reply to What does irreversible mean? (MAOI), posted by zarathustra on May 9, 2003, at 10:04:12

> I take parnate 20mg B.I.D.
>
> what does irreversible mean? Is it permanent?

Yes, (from the point of view of an individual molecule of the enzyme), but.... there's a lot more to it.

Every day, your body churns out enzymes. Also, every day, your body recycles enzymes back to their raw materials (amino acids and minerals, mostly). An individual enzyme molecule's life-span may be from 14-20 days (a generalization).

To artificially reduce an enzyme's activity, you may ingest inhibitors. Inhibitors come in many forms, which may be broadly categorized as irreversible or reversible. There are other ways of looking at them too, such as competitive or non-competitive, but I'll stick to the reversibility issue.

An irreversible inhibitor of an enzyme chemically changes its structure so that it can no longer function. That only applies to existing enzymes, because you'll recall that your body makes more of them every day. So, you have to take more of the inhibitor every day, to block the activity of the newly formed enzymes. Just for an example of an irreversible change in a protein (enzymes are proteins), consider hard-boiling an egg. There is nothing you can do to unboil it. The only alternative is to get another, fresh egg.

Reversible inhibitors (since we're taking about the enzyme MAO, an example is moclobemide (Aurorix, Mannerix)), work by an entirely different mechanism. They fit into the active site of the enzyme (where the chemistry takes place), but don't do anything else. Just by being there, they block access by the intended targets of the enzyme (in this case, neurotranmsitters dopamine, serotonin, and norepinephrine). An analogy might be a truck being blocked from parking in a loading zone because a car is parked there. The truck has to wait until the car leaves before it can enter its designated area.

Hope this helps,
Lar

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