The incorporation of radioactivity into polyols and carbon dioxide was measured for cultures of Dendryphiella salina incubated in media containing [i-14C]- or [6-14C]-glucose, with nitrate, ammonium or glutamate as nitrogen sources.
The labelling patterns show that mannitol is synthesized partly via a direct route from substrate glucose and partly from hexose-phosphate derived from the pentose-phosphate pathway. Rapid turnover of the mannitol pool and the redistribution of radioactivity caused by the symmetry of the mannitol molecule lead to the synthesis of labelled arabitol from both forms of radioactive glucose. After a 6-hour incubation period, the proportion of mannitol synthesized via the pentose-phosphate pathway ranges from 36% in nitrate media to 19% in glutamate media.
C1/C6 ratios for yields of 14CO2 also indicate that the activity of the pentose-phosphate pathway is greatest in the nitrate media and least in the presence of glutamate. Furthermore, there is an increase in the C1/C6 ratio when nitrate or methylene blue is added to cultures in ammonium media.
The results are discussed in relation to previous studies of the pentose-phosphate pathway in fungi containing mannitol.