THE CELL-WALL POLYMER OF THE EXTREMELY HALOPHILIC ARCHAEON NATRONOCOCCUS-OCCULTUS

Partial acid hydrolysis of the cell wall polymer produced soluble frag ments that could be separated by HPLC. A gamma-glutamyl dipeptide was isolated. In the intact cell wall polymer, the glutamate residues form a poly-(gamma-glutamine) chain with a length of about 60 monomers, wh ich corresponds to a relative molecular mass of approximately 7700 Da. Two other soluble dimeric fragments, composed of glutamate and either glucosamine or galactosamine in a molar ratio of 1:1, were purified f rom the hydrolysate, suggesting the presence of two different oligosac charides linked to the poly-(gamma-glutamine) chain of the intact poly mer. The analysis of additional fragments, which were composed of an a mino sugar and galacturonic acid or glucose indicated that one oligosa ccharide consisted of a glucosamine pentamer in an alpha-1,3 linkage a t the reducing end and an oligomer with at least five beta-1,4-linked galacturonic acid residues at the non-reducing end. The second oligosa ccharide was comprised of a galactosamine dimer in a beta-1,3 linkage at the reducing end and a maltose unit at the non-reducing end. Both o ligosaccharides were linked to the alpha-amide group of the glutamine residues of the poly-(gamma-glutamine) chain. The whole cell wall poly mer, which represents a novel type of natural glycoconjugate, has a re lative molecular mass of 54 kDa.