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Re: Feathers for S excretion...and tennis balls
I've found some time to write my final statements on this rather old
----- Original Message -----
Sent: Monday, April 02, 2001 10:08 PM
Subject: Re: Feathers for S excretion...and tennis balls
> Steve Brusatte writes:
> <Kidneys seem to suffice in modern mammals, even insectivorous ones. Do
> insectivorous mammals have more hair than carnivorous or herbivorous ones?
> Is the hair of insectivorous, and therefore sulfur-ingesting, mammals more
> laden with sulfur than the hair of carnivorous or herbivorous mammals?>
> I'm starting to feel we have whipped this dead horsefly as far as we can.
> Reason? Because the questions above are great ones -- given that insects
> a high source of sulfur. But somewhere about a million posts back, I hope
> mentioned the REAL reason I am so skeptical of this hypothesis.
> In the ten-thousand or so articles I have read (and written) in
> biochemistry, I have NEVER seen it mentioned that insects are anything
> than a NORMAL source of dietary sulfur. Where did Reichholf come up with
> basic datum anyway? I think it is wrong. Insects are NOT high sulfur
> creatures. And if that assessment is correct, then this whole thread is
> on . . . . . . . . . what?
I seem to have understood Reichholf incorrectly. In his second article
(1998) he doesn't say that there's exceptionally much _sulfur_ in insects.
He says there are lots of high-quality fat and _protein_ in insects --
quantity (of sulfur), not quality (high percentage of sulfur) --, which I
have read in several articles on why insects are good food for humans. In
the first one (1997), he states indeed (in the large chunk that I've
translated onlist) that "Insects contain, apart from fat, very much protein,
i. e. particularly sulfur-rich [protein]"; it is probable IMHO that the
cuticula proteins of insects contain more sulfur than other insect proteins.
Even if this is not true, I think the argument from the high percentage of
_protein_ in insects remains.
On sulfur excretion...
I have yet to look up how the taurocholic acid pathway works, among other
things. Can birds produce taurocholic acid?
So far, it seems reasonable to me to assume that mammals rely on sulfate
production and that birds can't easily excrete much sulfate. Concerning
water resorption in the cloaca, I should find out how this works and if it
can pull water off sulfate (pulling water off uric acid is surely easier).