Structural and Immunochemical Studies on D-Arabino-D-Mannans and D-Mannans of Mycobacterium tuberculosis and Other Mycobacterium Species1

Abstract

Serologically active D-arabino-D-mannas ([α]^D, +82°˜89°;ratio of D-arabinose to D-mannose, 1–2 : 1) were isolated from the soluble fraction of disintegrated cells of M. tuberculosis, M. smegmatis, and several other Mycobacterium species. These arabinomannans had similar structures, consisting of α-(1→5)-linked D-arabinose residues and α-(1→6)-, and (1→2)-linked D-mannose residues. Methylation and enzymic degradation studies using Arthrobacter sp. α-D-mannosidase and M-2 enzyme (D-arabinan hydrolase) indicated that the arabinomannan of M. tuberculosis Aoyama B possesses short side chains built up from α-(1→2)-D-mannosidic linkages which are attached to an α-(1→6)-linked mannan back-bone chain. The α-(1→5)-linked D-arabinose residues located in the side chains were shown, by comparison of the immunochemical activities of the native and enzyme-degraded polysaccharides, to be the main immunodeterminants, as in the cell-wall arabinogalactan. There appeared to be variations in the ratio of arabinose and mannose residues, and also in the proportion of (1→2)-linked D-mannose units, depending on the individual strain; no (1→2)-mannosidic linkage was found in M. smegmatis arabinomannan. In addition to arabinomannan, a serologically inactive α-D-mannan ([α]_D, +65°˜68°), whose structure may resemble that of the core mannan of the arabinomannan, was isolated as a copper hydroxide complex from the soluble fraction of disintegrated mycobacterial cells.