Characterization and regulation of glycine transport in Fusarium oxysporum var. lini

RESUMO

Glycine was transported in Fusarium oxysporum cells, grow on glycine as the sole source of carbon and nitrogen, by a facilitated diffusion transport system with a half-saturation constant(Ks) of 11 mM and a maximum velocity (Vmax) of 1.2 mM (g dry weight)-1 h-1 at pH 5.0 and 26 degrees Celsius. Under conditions of nitrogen starvation, the same system was present together with a high-affinity one(Ks) of about 47 muM and Vmax of about 60 muM (g dry weight)(-1) h-1)). The low-affinity system was more specific than the high-affinity system. Cells grown on gelatine showed the same behavior. In cells grown on glucose-gelatine medium, the low-affinity system was poorly expressed even after carbon and nitrogen starvation. Moreover, addition of glucose to cells grown on glycine and resuspended in mineral medium caused an increase of the glycine transport probably due to a boost in protein synthesis. This stimulation did not affect the Ks of the low-affinity system. These results demonstrate that, as is the case for other eukaryotic systems, F.oxysporum glycine transport is under control of nitrogen sources but its regulation by carbon sources appears to be more complex.