Uptake and metabolism of succinic acid by washed mycelium of Claviceps purpurea.

Washed mycelium of Claviceps purpurea exposed for 20 min to each of two external concentrations of 14C-succinic acid (0.035 and 0.0035 M) at pH 4.1 (54.3% H2-succinate, 43% H-succinate', and 1.4% succinate-2) accumulated radioactivity which, when expressed as succinic acid in cell water, was somewhat higher (0.046 and 0.0067 M) than the external concentrations. When exposed for 12 min, internal concentration of succinic acid based on isolated succinic acid was lower (0.024 M) than internal concentration based on total radioactivity (0.033 M). Only small amounts of succinic acid were respired and the remainder of mycelial succinic acid carbon was found in various mycelial constituents as lipids, mannose, mannitol, glutamate, glutamine, and residual mycelium. Time course experiments revealed that mycelial radioactivity obtained from external succinic acid increased during the first few minutes contact and then remained constant for at least 80 min. Uptake and accumulation at pH 4.1 is interpreted to be due to diffusion accompanied by metabolism until some limiting factor for metabolism is used up, and then to diffusion to approximate equilibrium with the outside. Uptake and accumulation or retention at pH 6.8 (0.01% H2-succinate, 4.8% H-succinate1-, and 95% succinate-2) was less than that occurring at pH 4.1 but was not simple adsorption as succinic acid carbon appeared in all fractions examined except residual mycelium. A comparison of both rate of uptake and total accumulation of succinic acid carbon at the two pH values suggested that uptake per se may not be influenced by ionization of succinic acid but that accumulation and retention against postwash may be. The amount accumulated or retained was inversely related to the per-cent of ionized carboxyl groups at these two pH values.