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Subject:
From:
Kathy Dettwyler <[log in to unmask]>
Reply To:
Lactation Information and Discussion <[log in to unmask]>
Date:
Sat, 27 May 2000 10:07:08 -0500
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Someone wrote:

>Casein has a species specific amino acid composition."  (p. 117 of her
book), but some
>peds are telling mothers to discontinue breastfeeding because "casein is
casein".  >Based on Lawrence, I disagree with this.  Am I right?

You are right, pediatricians are wrong (and it's scary to think that
pediatricians really believe "casein is casein").  That's like saying "milk
is milk" or "blood is blood."  Wouldn't want that doctor in charge of giving
me a blood transfusion!

Proteins vary from species to species depending on the amount of time since
the last common ancestor, plus different forces of natural selection and
gene flow and genetic drift operating on the different species once they
have diverged.  Hemoglobin is an excellent example.  Human and chimpanzee
hemoglobin is almost identical, but not quite, gorillas more different from
humans still, monkeys even more different -- by the time you get to a
comparison of say, horse and mouse and human hemoglobin, they are quite
different -- yet they are still all hemoglobin.

Within human hemoglobin, each molecule is made of two different types of
hemoglobin, alpha and beta, and each functioing protein contains 2 alpha
strands and 2 beta strands.  In people who have a *single amino acid
substitution* in the beta protein -- you find sickle-cell anemia.

All proteins are like this, varying to differing degrees from person to
person, and certainly from species to species.  Cows are not at all closely
related to humans, and their casein proteins are not identical.

Children sensitive to cows' milk casein *may or may not* be ALSO sensitive
to human milk casein.

Kathy Dettwyler

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