| Popis: |
The active transport of metabolites by Neurospora crassa conidia has been studied by both kinetic and genetic methods. Transport, reported to be dependent on temperature, pH, and an energy source, is shown to accumulate amino acids by (1) a system specific for neutral-aromatic amino acids, the neutral transport system; (2) a system specific for basic amino acids, the basic transport system; and (3) a non-specific general amino acid transport system. Transport by any of these systems, separately or in combination, results in the accumulation of the respective amino acid against a concentration gradient. The p -fluorophenylalanine-resistant mutant, Pm − N 22 , is deficient in transport of l -phenylalanine, but not l -arginine. Analogous to this is the canavanine-resistant mutant, Pm − B 37 , which is deficient in transport of l -arginine, but not l -phenylalanine. The double mutant, Pm − NB (derived from a cross of Pm − N 22 and Pm − B 37 ) has reduced transport of both l -arginine and l -phenylalanine. This double mutant retains some residual transport activity for both the basic and neutral amino acids. The kinetic properties of this residual activity indicate a capability for transport of either neutral or basic amino acids and further suggests that it is under separate genetic control. |
