Acidic pH stress induces protein tyrosine phosphorylation in Leishmania pifanoi

In order to determine whether in vitro Leishmania exposure to conditions comparable to those encountered inside the host cell would induce specific signals, we have studied tyrosine phosphorylation patterns in Leishmania pifanoi. Incubation of L. pifanoi at acidic pH resulted in the phosphorylation of several proteins including three of 27, 43 and 51 kDa, as well as the dephosphorylation of a 175 and a 39 kDa proteins in promastigotes recently transformed. In contrast, heat shock at 37 degrees C did not change the tyrosine phosphorylation pattern. Phosphorylation only occurs at pH 5.0 or lower and reached completion after 1 h. Changes returned to the initial conditions in 2 h after pH medium neutralization, indicating a reversible mechanism of phosphorylation.