Nucleoside-dependent protein kinase from Trypanosoma gambiense

Characterisation of protein kinase C like activities in Trypanosoma brucei

Protein kinase activities in bloodstream and procyclic forms of Trypanosoma brucei have been partially purified and characterised. Cytosolic extracts were separated on DEAE-cellulose and assayed for the ability to phosphorylate histone in the presence of Ca2+ and diacylglycerol. Five peaks of activity were identified in bloodstream T. brucei and only three in procyclic lysates. One of the kinases present in bloodstream T. brucei shares may characteristics with mammalian protein kinase C. Further characterisation of the kinases using an in situ assay after separating proteins by isoelectric focussing confirmed that the kinases present in bloodstream and procyclic stages differed in properties and either bloodstream kinases are more stable or greater in number than procyclic kinases. A protein present in bloodstream T. brucei was shown by Western blot analysis to contain an epitope recognized by a monoclonal antibody raised against mammalian protein kinase C. We thus conclude that the protein kinases are differentially regulated between the two stages of the parasite and that the bloodstream stage has a protein kinase C homologue. The implications of these findings in relation to a cellular signalling pathway in trypanosomes is discussed.

Nippostrongylus brasiliensis: occurrence of multiple protein kinases

The presence of cyclic AMP-dependent protein kinase and phosvitin kinases, with activity independent of cyclic nucleotides, was shown in the intestinal nematode Nippostrongylus brasiliensis. The activity of the cyclic AMP-dependent protein kinase was found to be enhanced about 8-fold in the presence of 10(-7) M cyclic AMP; the apparent Km values were determined to be 20 microM and 80 microM for ATP and kemptide, respectively. The molecular weight of the holoenzyme was about 170 000. Two phosvitin kinases could be isolated and distinguished by their molecular weights of 600 000 and 40 000. The activity of the high-molecular-weight phosvitin kinase was effectively inhibited by suramin and heparin. The apparent Km values were found to be 30 microM and 0.1 mg/ml for ATP and phosvitin, respectively. In the case of the low-molecular-weight phosvitin kinase the apparent Km values for ATP and phosvitin were found to be 30 microM and 0.6 mg/ml, respectively. The investigation of different developmental stages of N. brasiliensis revealed a marked higher level of protein kinase activity in the L4 larvae compared to L3 larvae and adults.

Cyclic AMP-dependent and independent protein kinases in Ascaridia galli

The occurrence of multiple protein kinases, distinguished with respect to molecular weight and preference for acceptor proteins, was demonstrated in Ascaridia galli. The molecular weights of the cyclic AMP-dependent protein kinase and of phosvitin kinase I and II - both independent of cyclic AMP-were determined to be 160000, greater than 200000 and 40000, respectively. The cyclic AMP-dependent protein kinase preferred histones and kemptide as acceptor substrates; stimulation of enzyme activity was up to 4-fold by cyclic AMP. The activities of phosvitin kinase I and II were found to be effectively inhibited by suramin. The inhibition constants were calculated to be 2 microM and 5 microM, respectively. In addition, stibophen turned out to be a potent inhibitor of phosvitin kinase I; the inhibition constant was determined to be 10 microM.

A plasmodium protein kinase that is developmentally regulated, stimulated by spermine, and inhibited by quercetin

Plasmodium berghei-infected murine red cells possess protein kinase activity that is associated with the isolated parasites. Schizonts contain significantly higher levels of this protein kinase than the more immature forms, suggesting a relationship between this enzyme activity and parasite development. Partially purified protein kinase has a Km for ATP of approximately 30 microMs, whereas the Km for GTP is approximately 300 microMs and the substrate preference is phosvitin greater than casein much greater than histone greater than protamine. The Mg2+ optimum is 10-20 mM, and the protein kinase activity is stimulated by the polyamines spermine and spermidine. The flavone, quercetin, inhibits the protein kinase activity in a competitive manner with respect to ATP (Ki approximately 3 microMs), and P chabaudi also has a very similarly regulated protein kinase. Protein kinases from both species are very similar to the type I casein kinase.

Subcellular distribution of adenylate cyclase, cyclic-AMP phosphodiesterase, protein kinases and phosphoprotein phosphatase in Trypanosoma brucei

The subcellular distribution of adenylate cyclase, cyclic-AMP phosphodiesterase, protein kinases and phosphoprotein phosphatase in bloodstream forms of Trypanosoma brucei was determined by isopycnic sucrose-gradient centrifugation of post-large-granule extracts. Cyclic-AMP phosphodiesterase was almost entirely soluble whereas adenylate cyclase was membrane-bound. The latter enzyme appeared to be absent from the plasma-membrane fraction but copurified with acid phosphatase and acid phosphodiesterase indicating a possible association with the flagellar pocket. At least two protein kinase activities could be distinguished as based on their distribution profiles in gradients, their preference for exogenously added acceptor protein and their inhibition and stimulation by suramin and nucleoside, respectively. Suramin-sensitive protein kinase co-purified with the plasma-membrane marker alpha-D-glucosidase and a nucleoside-stimulated protein kinase behaved as a typical cell-sap enzyme. Phosphoprotein phosphatase activity was found to be mainly soluble but a small part seemed to be associated with plasma membranes.

Effect of suramin on phosphorylation-dephosphorylation reactions in Trypanosoma gambiense

Suramin which is used as a chemotherapeutic agent against sleeping sickness was tested for its ability to inhibit phosphorylation-dephosphorylation reactions in Trypanosoma gambiense. Protein-kinase I, which is characterized by its preference for acidic acceptor proteins, was found to be strongly inhibited by suramin. The inhibition constant was calculated to be 0.8 microM. The type of inhibition was non-competitive with respect to ATP as well as to substrate protein.