Partial Release of Covalently Bound 18-Methyleicosanoic Acid from Wool Cuticle with Primary Alcohols

The stability of the bond of 18-methyleicosanoic acid (18-MEA) from untreated and chlorinated wool towards transesterification by alcohols was investigated. The extraction of untreated wool top with methanol not only dissolves the readily solvent-extractable lipids, but also the methyl esters of palmitic acid and 18-MEA from the cuticle proteolipids. About 10% of the total amount of 18-MEA is released by a 100 h Soxhlet-extraction with methanol from untreated top. With methanol replaced by ethanol, the ethyl esters of 18-MEA were detected. Transesterification of the 18-MEA proteolipids with the secondary alcohol 2-propanol was not observed. The treatment of wool with formic acid resulted in the removal of the soluble cell membrane lipids from the fibre but not in the release of 18-MEA. However, the removal of cell membrane compounds by solvents was shown to increase the accessibility of the 18-MEA-proteolipid regions for transesterification, and the influence of industrial chlorination is even more pronounced. These findings support the view that a significant part of the 18-MEA is bound to membrane domains of cuticular membrane proteins. The major portion of 18-MEA-containing proteolipids, however, is localized in areas of the fibre which are not accessible after modification of the cell membrane complex with solvents or by industrial chlorination.