REGULATION OF L-PROLINE TRANSPORT IN LEISHMANIA-DONOVANI BY EXTRACELLULAR PH

We have previously shown that Leishmania donovani promastigotes adapte d to long-term culture at acidic pH can serve as a model to study para site development in a lysosomal-like environment. In this study we inv estigated the effect of growth pH on L. donovani L-proline transport s ystems. Reducing the pH of the growth medium causes an up to 7-fold de crease in the extent Of L-proline transport. Transport resumes after s witching the culture from pH 4.5 to pH 7 for 48 h by a protein synthes is-dependent process. The pH optimum for transport changes from 7.5 in promastigotes grown at pH 7 to 5.5 in cells grown at pH 4.5. In addit ion, kinetic analysis of L-proline transport showed that V(max) in pH 4.5-grown L. donovani promastigotes is one-tenth that of cells grown a t pH 7 (4.5 and 44.7 nmol min-1 (10(8) cells)-1, respectively). The ap parent K(m) for L-proline in pH 4.5 promastigotes is one-half of the K (m) in pH 7 cells (0.30 and 0.65 mM, respectively). In contrast to L-p roline transport, D-glucose transport demonstrates a growth pH-indepen dent activity: K(m) and V(max) as well as optimum pH of transport are similar in promastigotes grown at either pH 7 or pH 4.5. Taken togethe r, the results indicate that in L. donovani, expression and activity O f L-proline transport is regulated by culture pH. The pH-dependent exp ression Of L-proline transporters may be of physiological significance during the promastigote-amastigote transition.