Spirit Collections: Accelerated Aging Studies concerning the Stability of Keratin in Ethanol and Formalin

-The keratins are a closely related family of chemically stable proteins composing mammalian hair, horn, hooves, and avian feathers . Sheep hair (wool) has been much studied chemically because of its economic value. To our knowledge, no studies have been conducted on the long-term stability of other keratins from a museum perspective. We present here differences in the stability of feathers and hair under simulated aging conditions. Feathers and hair were heated dry, in 70% ethanol, and in 70% ethanol plus 1 % formalin at 180°C for periods of 1 and 2 days. Feather keratin was approximately 50% less stable in ethanol than was hair keratin, as evidenced by the amount of amino acids lost from the sample and appearing in the solution. Feathers and hair, heated for the same periods of time under dry conditions, exhibited the same pattern of stability. As a corollary, the amino acid patterns of fresh hair and feathers from our samples of different species were found to be distinct and indicative of their originating taxon. The word "keratin" denotes a class of linear structural proteins that is characterized by disulfide bonds that link the sulfur atoms of two cysteine amino-acid residues. To a large degree, the stability of keratin is dependent on these bonds. Keratins are found primarily in the epidermal regions of vertebrate animals and function in a protecting capacity. This class of proteins encompasses the outer layer of skin, hair and fur, horn, nails (and hooves), feathers, and bird beaks (Yu et al. 1993). Keratins are pervasive in natural science and anthropological collections and are stored either "wet" or dry. Mammalian pelts and bird skins are stored dry, as are many cultural objects made from keratin. Entire bodies of animals and animal parts are maintained for research and taxonomic purposes. These are stored both as dried specimens and preserved in fluids. Despite this widespread presence in natural history museums, a protocol for keratin storage has yet to be developed. The variety of "dry" conditions includes storage at a constant room temperature and moderate relative humidity, as well as refrigeration in cold storage vaults at various temperatures and relative humidities. Fluid storage involves putting keratinous material in mixtures of reactive chemicals such as ethanol and formalin and often involves "topping off" when the level of liquid in the specimen container decreases from evaporation. This addition of fluid has an unknown effect on the possible leaching of chemicals from the specimen (von Endt 1994). For these reasons, and because the chemistry of keratin is relatively obscure, optimal storage conditions are unknown. The effects of such factors as temperature and water vapor must be researched and controlled to ensure the integrity of stored specimens and artifacts of scientific arid historical significance. Before optimal storage conditions can be determined, the nature of keratin itself must be examined. It is important to understand the chemical reactions undergone by kerCollection Forum 2000; 14(1-2):66-77 .----.-...~.~ --4IIIIf