Collagen composition in human skeletal remains from the NAX cemetary (A.D. 350-550) in lower Nubia
Collagen is an extremely stable protein that comprises 90% of the organic fraction of bone. Specific nutritional deficiencies and diseases are known to impair collagen synthesis and alter its typical amino acid composition. This study investigates the possibility that altered amino acid composition is evident in the pathological individuals of a large, well-preserved collection of archaeological remains.
Femoral cortical bone samples from 59 adults from the NAX cemetery (A.D. 350-550) near Wadi Halfa, Sudan, and five modern samples are examined for collagen preservation and amino acid composition. Elemental analysis of carbon, hydrogen, and nitrogen content indicates that protein preservation in the NAX samples is excellent. Only two have nitrogen contents below that of fresh bone, although seven samples display C/N ratios suggestive of diagenesis. Amino acid analyses, using both ninhydrin and OPA detection to obtain complete profiles, reveal depletion of the less stable amino acids (specifically, serine, methionine, isoleucine, tyrosine, and phenylalanine) and low levels of breakdown products in the NAX sample, which otherwise retains the characteristic composition of collagen.
Porotic hyperostosis in the Nubian population is a childhood condition stemming from iron deficiency anemia. It was anticipated that amino acids dependent on iron for their formation--hydroxyproline and hydroxylysine--would be depleted in this group in comparison to a nonpathological group, however, only phenylalanine is reduced significantly. The early onset of osteoporosis in the ancient Nubian population also is nutritionally linked, however, no significant differences are found. A final group comprised of individuals with both porotic hyperostosis and osteoporosis reveals a significant elevation of a breakdown product but no other differences.
The results indicate that differential degradation of amino acids occurs as a consequence of postmortem diagenesis. The lack of statistically significant differences attributable to pathology suggests that the biological stress was not chronic or severe enough to alter amino acid composition. Normal collagen synthesis appears to be maintained at the expense of mineralization.