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From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.med,sci.bio
Subject: Re: Dating age of humans
Message-ID: <2003@kitty.UUCP>
Date: Sat, 12-Sep-87 23:54:55 EDT
Article-I.D.: kitty.2003
Posted: Sat Sep 12 23:54:55 1987
Date-Received: Sun, 13-Sep-87 10:51:38 EDT
References: <26333@sun.uucp> <1960@kitty.UUCP> <3836@cit-vax.Caltech.Edu> <2195@sigi.Colorado.EDU>
Organization: Recognition Research Corp., Clarence, NY
Lines: 30
Keywords: Ageing Human Carbon
Summary: Age determination through racemization of amino acids
Xref: mnetor sci.med:3178 sci.bio:646

In article <2195@sigi.Colorado.EDU>, eddy@boulder.Colorado.EDU (Sean Eddy) writes:
> I am poorly informed on this, but a textbook of mine (it's a
> freshman text for a class I'm TA for) mentions briefly that you
> can date the age of a human by tooth enamel. No new protein is
> laid down in the tooth, so there is no amino acid turnover during
> one's lifetime. Amino acids are normally left-handed, but will
> slowly racemize and head for equilibration between right- and
> left- handed forms, if left alone like in tooth enamel (or
> in the crystallins on the lens of the eye). The book
> claims that a measure of right- vs. left-handedness in the amino
> acids of the tooth can provide a fair measure of one's age. 

	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.

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
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