Borate in mummification salts and bones from Pharaonic Egypt

Abstract

Mummification processes in Pharaonic Egypt were successful using sodium salts. Quite frequently sodium concentrations in mummified bones ranged from 300 to 4000 μmol/g. In the search for an effective inorganic conservation compound our choice fell on boric acid. The possible presence of borate in mummification salts used in Pharaonic Egypt was of special interest both historically and biochemically. In two salt samples, one from the embalming material of Tutankhamen (18th dynasty, 1336–1327 BC) and the second from Deir el-Bahari (25th dynasty, 700–600 BC) borate was found, amounting to 2.1±0.2 and 3.9±0.1 μmol/g, respectively. In five of the examined bone fragments from the Junker excavation at Giza (Old Kingdom) similar borate concentrations i.e., 1.2 μmol borate/g bone were seen. It must be emphasized that the usual borate content of contemporary autopsy is far below the detection limit. The elevated borate content in both mummification salt and ancient bone samples support the suggestion that borate-containing salt had been used. There is a striking correlation of both borate concentration and alkaline phosphatase activity. When both sodium salts and borate were essentially absent no activity at all was detectable. With increasing borate concentrations the enzyme activity rises significantly. Attributable to the distinct biochemistry of the tetrahydroxyborate anion it was of interest whether or not borate may stabilize alkaline phosphatase, an important and richly abundant bone enzyme. This enzyme was chosen, as it is known to survive more than 4000 years of mummification. In the presence of borate oligomeric species of this zinc-magnesium-glycoprotein at 400 000 Da became detectable. Attributable to this borate-dependent stabilization of the enzyme molecule a significant temperature resistant increase of the enzymic activity was measured in the presence of up to 2.5 mM borate.