The biosynthesis of galactofuranosyl residues in galactocarolose.

1. Cell-free extracts of Penicillium charlesii G. Smith were used in a study of the biosynthesis of the galactofuranose polymer, galactocarolose. 2. UDP-glucose and UDP-galactopyranose were precursors of galactocarolose and it was shown that the galactofuranose residues in the polymer were formed from glucose without fission of the hexose carbon chain. 3. A new nucleotide, UDP-alpha-d-galactofuranose, was formed by the system and was a major product when polymer synthesis was inhibited by F(-) or Zn(2+); the nucleotide was isolated and its structure determined. 4. UDP-alpha-d-galactofuranose was efficiently utilized for polymer synthesis and shown to be formed from the pyranose nucleotides. 5. A route for the biosynthesis of galactocarolose, involving a novel ring contraction of the hexose residue while still attached to the nucleotide, is proposed.