Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!pyramid!hplabs!oracle!rbradbur
From: rbradbur@oracle.UUCP (Robert Bradbury)
Newsgroups: sci.bio
Subject: Death defying dehydration and the meaning of "life"
Message-ID: <245@oracle.UUCP>
Date: 18 Feb 88 13:34:03 GMT
Organization: Oracle Corporation, Belmont, CA
Lines: 36
Keywords: life, death, dehydrate, freezing

The Feb 13 issue of Science News has a very interesting article about
life forms (nematodes, brine shrimp, tardigrades) which can "live"
after "death" by dehydration.  The gist of the article is that
these animals have evolved a bio-chemistry which allows them
to be de-hydrated to the point that metabolism *may* cease.  They
can be re-hydrated after 5 to 120 years and return to "life".
The survival rates for 5 year dehydration of nematodes is 80-90%.

The bio-chemistry seems to be fairly simple in that high concentrations
of trehalose (a two glucose ring sugar) keep lipids (in cell walls)
from breaking down and trehalose in combination with zinc protects
proteins and enzymes.  The sugar prevents damage when the water
is removed by "locking" the lipids and proteins in their "hydrated"
shape.  They can then be re-hydrated without much damage.

This leads to some interesting questions:

 - If metabolism stops in de-hydrated life forms have they "died"?
   One of the researchers (John Crowe - UC Davis) proposes that the
   definition for "life" might have to be simply "organized structure".
   If that is true then are mineral crystals or computer chips alive?

 - If the survival rates of these animals is so high are efforts to
   preserve organs/human beings by freezing somewhat misdirected?
   Shouldn't the process be to bathe the tissues in a trehalose
   and zinc solution, de-hydrate and then freeze?

I'm a fairly strong believer that science is going to eventually
solve the freezing/re-animation problem and would be interested
in views on that impact on society (insurance, wills, religion, etc).
(We might want to move such things to a more appropriate group though.)


-- 
Robert Bradbury
Oracle Corporation
(206) 784-9726                            hplabs!oracle!rbradbur