Transport of C 4 -dicarboxylic acids in Neurospora crassa

1. 1. The transport of tricarboxylic acid cycle dicarboxylic acids by Neurospora crassa was induced 80-fold by growth on acetate whereas tricarboxylic acid enzymes were induced only 2-6-fold and glyoxylate cycle enzymes were induced 20-fold. 2. 2. From the kinetics of uptake and competitive inhibition it was concluded that a single system was responsible for the transport of succinate, fumarate, l-malate and possibly α-ketoglutarate as well as a number of structural analogues. The system appears to be less specific than the known bacterial systems. 3. 3. Succinate transport was strongly inhibited by various known inhibitors of energy metabolism — primarily by proton conductors. Transport was also severely inhibited by various sulfhydryl reagents. 4. 4. Succinate, fumarate and l-malate uptake were identically pH dependent and evidence is presented which implicates the monoionic species as the molecular form of the dicarboxylic acid transported.