title: Extracellular phosphorylation in the parasite, Leishmania major.
abstract: Intact promastigotes or cell-free extracts of the parasite Leishmania major were labelled with adenosine 5'[gamma-32P]-triphosphate (ATP). This resulted in the identification of eleven phosphoproteins. [gamma-32P]ATP incorporation into endogenous and exogenous substrates was insensitive to most of the commonly used protein kinase inhibitors and activators indicating that the leishmanial enzyme(s) may represent a new class of kinase(s). In addition, exogenous substrate specificity was inconsistent with the preferences of second messenger-dependent protein kinases. Cyclic AMP had differential effects on phosphorylation in intact cells and lysates. The majority of kinase activity could be attributed to an externally oriented membrane-associated protein kinase(s), as no specific cytosolic phosphoproteins were found and intact cells phosphorylated exogenous substrates. Labelled ATP did not cross the membrane and [alpha-32P]ATP was an unsuitable substrate for the phosphorylation activity. The ectokinase activity on live Leishmania exhibited a different substrate preference when compared to the protein kinase activity in the particulate fraction, suggesting that more than one protein kinase may be present in L. major. Three serine-labelled phosphoproteins were specifically released into the medium. The presence of an ecto-kinase and these released phosphoproteins may play a significant role in host-parasite interactions.
authors.affiliation: Department of Membrane Research, MacArthur Center for Molecular Biology of Tropical Diseases, Weizmann Institute of Science, Rehovot, Israel.
authors.forename: D S
authors.initials: DS
authors.lastname: Lester
authors.forename: T
authors.initials: T
authors.lastname: Hermoso
authors.forename: C L
authors.initials: CL
authors.lastname: Jaffe
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002474:Cell-Free System; D007895:Leishmania tropica / Q000201:enzymology / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D010750:Phosphoproteins; D000255:Adenosine Triphosphate; D011494:Protein Kinases