Kinetic parameters of erythrocyte L-tryptophan (TRP) uptake (Vmax, maximal velocity and Km, Michaelis constant) were determined in 19 neuroleptic-free schizophrenic patients and in 19 healthy volunteers. Both Vmax and Km values were significantly lower in schizophrenic patients than in controls. 2. Mean Vmax value was found to be lower in patients who had attempted suicide than in patients who had not. No difference was observed when patients were subdivided on the basis of the violence of suicide attempts. 3. A significant negative correlation was observed between Vmax and scores on the loss of impulse control item as assessed on the PANS scale. 4. Decrease in red blood cell L-TRP uptake reflects a disturbance in the peripheral metabolism of TRP that may result in a deficiency of the plasma L-TRP availability on which the central serotonin (5HT) synthesis closely depends. 5. In addition, the results suggest that the alteration in RBC L-TRP uptake is associated with loss of impulse control in schizophrenic patients.
