CHARACTERIZATION AND REGULATION OF GLYCINE TRANSPORT IN FUSARIUM-OXYSPORUM VAR LINI

Glycine was transported in Fusarium oxysporum cells, grown on glycine as the sole source of carbon and nitrogen, by a facilitated diffusion transport system with a half-saturation constant (K-s) of 11 mM and a maximum velocity (V-max) of 1.2 mM (g dry weight)(-1) h(-1) at pH 5.0 and 26 degrees C. Under conditions of nitrogen starvation, the same sy stem was present together with a high-affinity one (K-s) of about 47 m u M and V-max of about 60 mu M (g dry weight)(-1) h(-1)). The low-affi nity system was more specific than the high-affinity system. Cells gro wn on gelatine showed the same behavior. In cells grown on glucose-gel atine 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 K-s of the low-affinity system. These results demonstrate that, as is the case for other eukaryotic sy stems,li. oxysporum glycine transport is under control of nitrogen sou rces but its regulation by carbon sources appears to be more complex.