Fig. 5.

Schematic outline of mannan biosynthesis. Hexose phosphates derived from the glycolytic, gluconeogenic, and pentose phosphate pathways are converted to Man-6-P and Man-1-P. Man-α-1-P can be converted to either the mannan chain primer (ManP_c) or to GDP-Man, the donor for mannan chain assembly. The conversion of Man-α-1-P to ManP_c is predicted to be energetically unfavorable and to involve an as-yet-unidentified activated species (denoted by the brackets). Man_nP_c species containing four to five Man residues are dephosphorylated and further elongated by sequential additions of single Man residues. (Inset) Structure of Man-α-1,4-cyclic P primer.