Uptake of ¹⁴C-Labelled Succinate, L(+)-Dihydroxysuccinate, L-Monohydroxysuccinate, Citrate, Alpha-Ketoglutarate, and D-Glucose by Washed Mycelium of Claviceps Purpurea

SUMMARY

Plotting uptake of ¹⁴C-succinic acid as a function of time produced curves of two phases separated by a lag phase. The first phase which lasted for 1–3 min was probably diffusion uptake because it was affected little, if at all, by pH, temperature, concentration of succinate, sodium azide, iodoacetate, or the presence of any of the following unlabelled organic acids in both the prewashes and reaction mixture: succinic, alpha-ketoglutaric, citric, L(+)-dihydroxysuccinic, or L-monohydroxysuccinic. Preloading the mycelium with succinate did not affect first phase uptake. The second phase is continuous accumulation of succinic acid carbon and was prevented or retarded by azide, high concentrations of succinate, and equimolar amounts of the above mentioned organic acids. The two phases were usually separated by a short lag period at pH 4.1 and by a longer lag at pH 6.8 (acid mostly dissociated). Both phases were slower at pH 6.8. Heat-killed mycelium displayed first phase uptake similar to that of azide-treated mycelium. Uptake and accumulation of ¹⁴C-glucose was the same at pH 4.1 and 6.8. Uptake and accumulation of succinate was the same whether the mycelium was previously grown in the presence or absence of succinate or in the presence or absence of glucose. Glucose added to the reaction mixture did not affect uptake and accumulation of succinic acid. Mycelium exposed to ¹⁴C-labelled alpha-ketoglutarate, citrate, dihydroxysuccinate, or monohydroxysuccinate for up to 15 min displayed only first phase uptake followed by the plateau.