Uptake and translocation of 2-aminoisobutyric acid bySchizophyllum commune

The nonnative amino acid, 2-aminoisobutyric acid (AIB), is transported into homokaryotic mycelia ofSchizophyllum commune. However, because it is neither incorporated into protein nor further metabolized by the fungal cells, it may be used as a marker for the free amino acid pool. Colonies grown or maintained under nitrogen-limiting conditions show enhanced uptake and higher concentrations of AIB in the mycelium than controls. Based on growth inhibition and uptake kinetic experiments, the enhanced uptake appears to be the result of decreased competition for a common uptake channel withl-asparagine normally found in the medium. Colonies containing radiolabeled AIB show translocation of the label to growing hyphal apices when they are transferred to unlabeled nitrogen-deficient media. Chases on nitrogen-rich media do not result in translocation of the label. In contrast to colonies chased on nitrogen-rich media, nitrogen deprivation does not lead to release of significant amounts of AIB into the medium by older cells. This supports an intramycelial pathway for translocation of pool amino acids.