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From: eddy@boulder.Colorado.EDU (Sean Eddy)
Newsgroups: sci.med,sci.bio
Subject: Re: Dating age of humans
Message-ID: <2199@sigi.Colorado.EDU>
Date: Sun, 13-Sep-87 10:28:16 EDT
Article-I.D.: sigi.2199
Posted: Sun Sep 13 10:28:16 1987
Date-Received: Sun, 13-Sep-87 21:39:32 EDT
References: <26333@sun.uucp> <1960@kitty.UUCP> <3836@cit-vax.Caltech.Edu> <2195@sigi.Colorado.EDU> <2003@kitty.UUCP>
Sender: news@sigi.Colorado.EDU
Reply-To: eddy@boulder.Colorado.EDU (Sean Eddy)
Organization: University of Colorado, Boulder
Lines: 32
Keywords: Ageing Human Carbon
Xref: mnetor sci.med:3183 sci.bio:647

In article <2003@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes:
>	I am slightly familiar with the chemistry behind dating bones
>through racemization.  However, I have only seen this applied to
>archeological specimens with ages from hundreds of years to 100,000+ years.
>	In this application, isoleucine is one amino acid that is used;
>it has a racemization "half-life" of something like 100,000 years at
>ambient temperature.  The racemization is L-isoleucine <--> D-alloisoleucine.
>	L-aspartic acid is also used; it has a "half-life" of something
>like 15,000 years at ambient temperatures.  The racemization here is
>L-aspartic acid <--> D-aspartic acid.  
>	In view of the long racemization "half-life" times of the above
>amino acids, I have doubts that any other suitable amino acid would
>racemize in a short enough time to provide a useful resolution in living
>subjects.

Ah, yes. I told you I didn't know what I was talking about.
Thanks for the clarification...

...but I'm not satisfied yet. My wonderful little biology text
(which I hate, so I don't care if it's wrong) tries to convince
me that dating by racemization is being used to check the validity
of claims to incredible old age, such as those made by these people
in Peru or the Caucasus. Perhaps some amino acids have reasonably
short racemization half-times? Or alternatively, detection of
D-amino acids is very precise (since there are absolutely none
whatsoever in the protein to start with, any D-amino acid
constitutes signal and not background)?


- Sean Eddy
- MCD Biology; U. of Colorado at Boulder; Boulder CO 80309
- eddy@boulder.colorado.EDU		!{hao,nbires}!boulder!eddy