PROTEIN-TYROSINE-PHOSPHATASE ACTIVITY IN LEISHMANIA-DONOVANI

L. Donovani promastigotes were grown to late-log and 3-day stationary phase to determine the level of protein tyrosine phosphatase activity in crude extracts and in fractions following gel filtration column chr omatography. Over 90% of the activity was soluble in a low salt extrac tion buffer in both phases of growth. Several peaks of activity were r esolved following gel filtration of the crude extracts indicating that multiple tyrosine phosphatases are present in these cells. Tyrosine p hosphatase activity was lower in 3-day stationary than in late log-pha se cells and a reduction in the major peak of activity, eluting in a g el fraction corresponding to an M(r) of approximately 168 kDa, was obs erved. In vivo tyrosine phosphorylation was revealed by Western blot a nalysis. The degree of phosphorylation of at least two proteins differ ed in cells obtained from late log phase cultures as compared with 3-d ay stationary phase cultures. These observations indicate that changes in the balance between tyrosine phosphorylation and dephosphorylation occur with increasing culture age.