Comparison of adenylate cyclase and cAMP-dependent protein kinase in gametocytogenic and nongametocytogenic clones of Plasmodium falciparum.
Adenylate cyclase and cAMP-dependent protein kinase activities in gametocytogenic (LE5) and nongametocytogenic (T9/96) clones of Plasmodium falciparum were compared to explore the role of cAMP in sexual differentiation of the parasite. Basal adenylate cyclase levels were equivalent in the 2 clones. However, cAMP-dependent histone II-A kinase activity was significantly higher in LE5 than in T9/96 over a range of cAMP concentrations. This difference was due to a decreased Vmax for the enzyme in the nongametocytogenic clone and not to an increased Ka for cAMP. Examination of parasite cAMP-binding proteins, likely to be kinase regulatory subunits, by both photoaffinity labeling with [32P]8-N3-cAMP and affinity chromatography of metabolically [35S]methionine-labeled cytosol of cAMP-agarose revealed a 53-kDa cAMP binding protein in both clones and a 49-kDa cAMP-binding protein in T9/96 that was absent in LE5. Our results suggest that T9/96 has lost the ability to undergo gametocytogenesis due to a substantial decrease in cAMP-dependent protein kinase activity rendering the parasite unable to respond to increased intracellular cAMP levels. Moreover, the reduction in cAMP-dependent protein kinase activity may be due to the presence of an alternative regulatory subunit of the kinase.
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Tufts University School of Medicine, Department of Physiology, Boston, Massachusetts 02111.
Mikkelsen
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D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002846:Chromatography, Affinity; D003720:Densitometry; D005718:Gametogenesis / Q000502:physiology; D010963:Plasmodium falciparum / Q000201:enzymology* / Q000502:physiology; D011494:Protein Kinases / Q000378:metabolism*
D011494:Protein Kinases; D000262:Adenylyl Cyclases