title: Wet degradation of keratin proteins: linking amino acid, elemental and isotopic composition.
abstract: BACKGROUND
  Archaeological keratin samples are increasingly the subject of palaeodietary, provenancing and dating studies. Keratin samples from wet archaeological contexts are microbiologically and chemically degraded, causing differential diagenesis of protein structures in hair fibres. The effects of these processes on the analytical parameters of interest are currently unknown.
  
  
  METHODS
  This study examined the impact of degradation of wool fibres on isotopic (δ(13)C, δ(15)N, un-exchangeable δ(2)H and δ(18)O values) composition. It compared two models of archaeological protein degradation in wet burial environments: (1) short term (up to 8 years) experimental burial in three contrasting soil environments; and (2) laboratory wet conditions, in which elevated temperature (80 °C, 110 °C, and 140 °C) and pressure simulated longer exposure. Elemental and amino acid (AA) composition were also measured.
  
  
  RESULTS
  In experimentally soil-buried samples, AA, elemental and isotopic composition changes were small, despite extensive macroscopic alteration. Isothermally heated samples showed preferential loss of hydrophilic AAs (Asx, Glx, Ser, Gly) from wool residues, with depletion in (2)H and (18)O at higher temperatures (up to -73‰ change in δ(2)H and -2.6‰ in δ(18)O values). The δ(13)C and δ(15)N values showed little change except in densely pigmented samples at low temperatures only. Samples dyed with madder/alum were better preserved than undyed samples.
  
  
  CONCLUSIONS
  Diagenesis in experimentally soil-buried wool textiles was consistent with microbiological, non-protein-selective activity, in contrast to highly AA-selective hydrolytic behaviour under laboratory wet conditions. Changes in δ(2)H and δ(18)O values were correlated with degree of AA change, but the δ(13)C and δ(15)N values were not. The results contribute to a baseline for interpreting analytical data from archaeological hair samples preserved by burial in wet environments.
authors.affiliation: BioArCh, Departments of Archaeology and Chemistry, University of York, Heslington, York, YO10 5DD, UK.
authors.forename: I C C
authors.initials: IC
authors.lastname: von Holstein
authors.forename: K E H
authors.initials: KE
authors.lastname: Penkman
authors.forename: E E
authors.initials: EE
authors.lastname: Peacock
authors.forename: M J
authors.initials: MJ
authors.lastname: Collins
mesh_terms: D000596:Amino Acids / Q000032:analysis* / Q000737:chemistry; D000818:Animals; D001106:Archaeology; D002048:Burial; D002851:Chromatography, High Pressure Liquid; D007554:Isotopes / Q000032:analysis; D007633:Keratins / Q000032:analysis / Q000737:chemistry*; D013058:Mass Spectrometry; D008956:Models, Chemical; D012756:Sheep; D013696:Temperature; D013997:Time Factors; D014935:Wool / Q000737:chemistry
chemical_list: D000596:Amino Acids; D007554:Isotopes; D007633:Keratins