Assimilation of Xylose, Mannose, and Mannitol for Synthesis of Glucuronoxylomannan of Cryptococcus neoformans Determined by (13)C Nuclear Magnetic Resonance Spectroscopy

Cryptococcus neoformans NIH 409 was cultured in a defined medium containing d-[1-(13)C]xylose (Xyl), d-[1-(13)C]mannose (Man), or d-[1-(13)C]mannitol as the sole carbon source. The distribution of (13)C in the Man, Xyl, glucuronic acid (GlcA), and O-acetyl constituents of native and de-O-acetylated glucuronoxylomannan (GXM) was determined by one-dimensional (13)C nuclear magnetic resonance spectroscopy. The carbon chain of Man was incorporated intact into GXM since (13)C was observed only in carbon 1 of Man, GlcA, and Xyl. The carbon chain of mannitol was incorporated intact into GXM since (13)C was observed only in carbons 1 and 6. This was expected since mannitol has an axis of symmetry. The carbon chain of Xyl was identified only in carbons 1 and 3 of Man, GlcA, and Xyl. This pattern of labeling is consistent with the assimilation of Xyl through the pentophosphate pathway.