Why can't doctors simply add the enzyme that is deficent in PKU to the individuals diet?

Question

Just a student who is confused by what he was told about the disease. I do not see why the enzyme could not be regularly added to diet.

When you say gut would break it apart do you mean the stomach acids?
Why not try pills or something?

Answer 1

Your gut would break it apart before the body could use it.

Answer 2

While I cannot say anything with any degree of certainty, I do have lots of random guesses!

First I think you have to realize that in the gastrointestinal tract most proteins are quickly broken up into their component parts, those wonderful peptides. In fact, most of the protein your body absorbs from a meal is in the form of mono-, di-, and tri -peptides (meaning there's only one, two, or three of 'em hooked together.) Considering the fact that most enzymes require frequently dozens of peptides to function, the chance of an enzyme ingested surviving its trip through the stomach is small.

You do bring up a potentially interesting way to getting around that, however. Many pills these days are in fact coated with materials that allow them to bypass much of the initial digestion/absorption in the stomach. The problem is protein digestion does not end there. The small intestine though not rich in acid is rich in various protein cleaving molecules of its own.

Supposing the enzyme in question somehow does survive the gauntlet of the GI tract, that doesn't necessarily mean it will be absorbable by the intestines. It may in fact be too large or have some serious polarity issues preventing its acquisition.

Of course, if theoretically the enzyme could do its work fast enough you could hypothetically give it in high enough doses during each meal to degrade any possible phenylalanine in the diet, but the mechanics of that are likely not as practical or realistic as they sound. This is assuming, too, that the enzyme does not need any cofactors or ATP or anything else to spur it along in its peptide hydroxylating job.

Basically, as with most drugs, there's lots of things that can go wrong and lots of things that need to go right for it to work. Chances are any one or series of problems could exist. This is not to say that this or anything I've said is in fact the case, but I think they're all possibilities. And of course perhaps none of these are problems at all and researchers are in fact trying this out right now. Somewhere little white phenylalanine hydroxylase deficient mice may be eating little white enzyme pills and ushering in a brave and glorious future. For people with PKU at least.

And I've already spent too long on a question I don't necessarily know anything about. The end!

Answer 3

because they are idiots......