Characterization of 18-Methyleicosanoic Acid-containing Proteolipids of Wool

Abstract

Proteolipids containing 18-methyleicosanoic acid (18-MEA) were dissolved from the enzymatically isolated cell membrane complex fraction (CMC) of wool and characterised by different techniques. Prior to the enzymatic digestion of the wool, the major part of the noncovalently bound lipids, including a remarkably high proportion of the 18-MEA in the wool (27 wt% of the total amount of 18-MEA) was removed by extraction with chloroform. About 12 wt% of 18-MEA was directly accessible for extraction with chloroform from the CMC. The main part of it remained covalently attached to proteinaceous CMC material. By treatment of the CMC with a two-phase solvent system, proteins dissolved in the aqueous phase, proteolipids dissolved in the organic phase, and an insoluble extraction residue was obtained. The hydrophobic character of the proteolipids is caused by their high content of covalently bound fatty acids, mainly 18-MEA, and a high portion of non-polar amino acid residues. The proteolipids were further purified by countercurrent chromatography, and a hydrophobic protein fragment with significantly high amounts of cystine and serine, potential partners for an ester or thioester linkage with fatty acids, was isolated. A comparison of the amino acid compositions of the three CMC fractions to those of morphological components of wool, by means of cluster analysis, gives strong evidence that the proteolipids are a part of the CMC δ-layer.