At a widely publicized news conference in August of 1972, Dr.
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The rates obtained at these temperatures were extrapolated to 2° C and to 4° C, the present average temperatures where the deep-sea cores containing the sediment samples were obtained.
These data are believed to yield the rates at which L-isoleucine was converted to Dalloisoleucine in the sediment through geological time.
The D-form tends to revert to the L-form, and eventually an equilibrium is obtained, as illustrated here for alanine: Mixture of equal amounts of the L- and D-forms, The process by which an L-amino acid changes into a mixture of the L- and D-forms (or the D-form changes into a mixture of the L- and D-forms) is called racemization.
Racemization is complete when equal amounts of the L- and D-forms are obtained.
When there is only a single asymmetric carbon atom, these two different forms are known as optical isomers.
Chemically, there is very little difference between them, but biologically, there is as much difference as night and day.
Later, Bada and his co-workers the rate of racemization in marine sediments under laboratory conditions was determined by heating sediments with sea water in sealed ampoules at various temperatures from 100° C to about 150° C over various lengths of time.
The material was then hydrolyzed in 6 molar hydrocholoric acid (the material is hydrolyzed to break up the protein into free amino acids), and the extent of conversion of L-isoleucine to D-alloisoleucine was determined.
He was quoted as saying that he had discovered the basis of the method in 1968, and that it was so obvious and simple he was amazed it hadn't been discovered earlier.
As a matter of fact, the basis of this method had been discovered earlier and had been reported in a series of papers published by Hare, Mitterer and Abelson in 1967, 1968, and 1969.
Thus, the older a fossil shell or bone, the greater should be the extent of racemization of the amino acids which are contained in the proteins found in the bone or shell.