Age at death determinations for autopsied remains based on aspartic acid racemization in tooth dentin: importance of postmortem conditions.

The extent of aspartic acid racemization in human dentin can be used to assess chronological age of the individual. This novel chemical method of aging human remains has potential applications in forensic sciences. Six autopsy cases have been analyzed for D/L aspartic acid contents, and their ages at death calculated. Independent age information came from known identity, tooth maturation, or tooth wear estimations. The six cases represented a range of postmortem fates: recent demise, burial, and ground surface exposure. Five samples, four recently deceased and one a burial, showed racemization ages in close agreement with other age data. One specimen, subjected to 51 days of open air exposure, exhibited a vastly inflated racemization age. Postmortem conditions are crucial to the accuracy of racemization age at death measurements.

In vivo decomposition of phosphoserine and serine in noncollagenous protein from human dentin.

HCl-soluble proteins in human dentin ranging in age from 3 to 45 years exhibit amino acid compositional changes consistent with beta-elimination and hydrolysis of phosphoserine as well as dehydration and aldol cleavage of serine. This is the first evidence of nonenzymatic mechanisms for in vivo degradation of hydroxy and substituted hydroxy amino acids in dentin. Decomposition of phosphoseryl residues reduces the calcium-binding capacity of phosphoproteins. Elimination and dehydration reactions can produce variability in molecular weight. The rates of decomposition may be rapid enough to cause the heterogeneity or "maturational" degradation seen in dentin phosphoproteins during mineralization.

Protein-alkali reactions: chemistry, toxicology, and nutritional consequences.

Heat and alkali treatment of proteins catalyzes formation of crosslinked amino-acid side chains such as lysinoalanine, ornithino-alanine and lanthionine, and concurrent racemization of L-isomers of all amino acid residues to D-analogues. Factors that favor these transformations include high pH and temperature, long exposure, and certain inductive or steric properties of the various amino acid side chains. Factors that minimize crosslink formation include the presence of certain additives, such as cysteine or sulfite ions, and acylation of epsilon-NH2 groups of lysine side chains. Free and protein-bound lysinoalanine and D-serine induce nephrocytomegaly in rat kidney tissues. The presence of lysinoalanine and D-amino acid residues along a protein chain decreases its digestibility and nutritional quality. Understanding the factors that govern the formation of potentially harmful unnatural amino acid residues in food proteins and the toxic and nutritionally antagonistic action of these compounds in animals should lead to better and safer foods.

Stereochemically altered noncollagenous protein from human dentin.

Highly phosphorylated noncollagenous proteins (NCP) with molecular weights of approximately 70-100,000 daltons have been purified from rat and bovine dentin. Efforts to isolate phosphoprotein from human teeth have not yielded consistent results, and failures have been attributed to proteolysis due to preparative techniques. Diagenetic reactions affecting metabolically stable proteins in vivo also can interfere in protein purification. Racemization is one of the reactions known to take place in human dentin. EDTA extraction of dentin from an age-graded series of human teeth has yielded an EDTA-soluble NCP fraction having an aspartic acid racemization rate 3 X that in unfractionated dentin and 8 X the rate in EDTA-insoluble protein. D-Aspartic acid is accumulating in EDTA-S protein at a rate of 0.22% yr-1. For humans, more than 13% of the aspartyl residues in NCP will be the D-enantiomer by 60 years of age. While racemization presents no problem for shorter lived mammals, such as rats, it could be partly responsible for purification difficulties with human dentin.

Age determination of an Alaskan mummy: morphological and biochemical correlation.

Aspartic acid racemization analysis of a tooth from an Alaskan mummy yielded an age at death of 53 (+/- 5) years, which correlates well with earlier estimates based on morphological features. This study illustrates the value of integrative approaches to paleopathologic problems and the importance of preserving rare specimens for the application of new techniques.

Aspartic acid racemization in heavy molecular weight crystallins and water insoluble protein from normal human lenses and cataracts.

High D/L aspartic acid ratios are observed in heavy molecular weight aggregates and in water-insoluble protein extracted from whole lenses and nuclear and cortical regions. Purified alpha-, beta-, and gamma-crystallins have low D/L ratios. Fractionation of urea-solubilized material from the water-insoluble protein yields four molecular weight classes of proteins. Fractions representing crosslinked material or apparently degraded products have high D/L ratios. Racemization within lens proteins may contribute to formation of the water-insoluble fraction seen in aging lenses and cataracts.