An Inhibition and Kinetic Study of Acid Phosphatase inParamecium caudatumandParamecium tetraurelia1

Phosphohydrolytic activity in Paramecium caudatum at neutral pH

Phosphohydrolytic activity was cytochemically characterized in Paramecium caudatum, a ciliated protozoa, at neutral pH. We stained cells in the presence of several mononucleotides as substrates, namely adenosine 5'-monophosphate (5'-AMP), adenosine 2'-monophosphate, guanosine 5'-monophosphate (5'-GMP) and beta-glycerophosphate (beta-GLP) using a lead capture method at 37 degrees C. Cells were also incubated in the presence of 5'-AMP with the inhibitor for alkaline phosphatase, tetramisole. In all cases, varying amounts of final reaction product, lead sulfide, was observed in Paramecium cytoplasm. Tetramisole did not have any effect on Paramecium 5'-AMP hydrolytic activity. The phosphohydrolytic activity was measured as the increase in total absorbance of "test minus control" reactions at 440 nm per unit time after 20 min of incubation using a microphotometric system for image analysis that has been developed by us. From the relationship between the concentrations of 5'-AMP and activity, an apparent K(m) value was estimated to be 0.20 mM. These results suggest that mononucleotides and phosphate monoesters are hydrolyzed by one or more enzymes with wide substrate specificity in P. caudatum. All the activity distribution patterns in Paramecium cultures, that were tested, were monomodal. The mean activity for 5'-AMP hydrolysis widely varied in these cultures. To investigate substrate affinity, distribution patterns and mean activity with 5'-AMP as substrate were compared with those in the presence of 2 other substrates, 5'-GMP and beta-GLP. Affinity of the enzyme(s) was similar for 5'-AMP and 5'-GMP and lower for beta-GLP.

Occurrence of a para-nitrophenyl phosphate-phosphatase with calcineurin-like characteristics in Paramecium tetraurelia

Using para-nitrophenyl phosphate (pNPP) as a substrate for enzymatic activity, we sought to identify CaN in Paramecium. We isolated three different pNPP-phosphatases from the soluble fraction of Paramecium cells by anion-exchange and affinity column chromatographies. One, pNPP-phosphatase Peak I, is very similar to mammalian CaN. Divalent cation dependency, inhibition by calmodulin (CaM) antagonists (trifluoperazine, calmidazolium), and insensitivity to various phosphatase inhibitors (heparin, okadaic acid, sodium vanadate, etc.) show similarity to mammalian CaN rather than to any other Paramecium pNPP-hydrolyzing enzymes tested. Polyclonal antibodies against bovine brain CaN recognizing subunits A (61 or 58 kDa) and B (17 kDa) of brain CaN cross-reacted with a 63-kDa protein in fractions containing Peak IpNPP-phosphatase activity and coeluted calmodulin. Overlay assays using biotinylated brain calmodulin indicated Ca2+-dependent CaM-binding by the 63-kDa protein. A Ca2+-binding protein with the same electrophoretic mobility as CaN B (17 kDa) was also present, though in other fractions from DEAE-cellulose chromatography. This finding strongly suggests that, in the absence of Ca2+, both subunits, A and B, were separated either before or during chromatographic processing. Our data support the existence of both subunits of a CaN-like phosphatase in Paramecium cells.

Isolation of the membranes from secretory organelles (trichocysts) of Paramecium tetraurelia

We present for the first time a method for isolation of the membranes of extrusive organelles (trichocysts) from sterile culture of different strains of Paramecium tetraurelia. First, trichocysts are isolated according to a new method (Glas-Albrecht, R. and Plattner, H. (1990) Eur. J. Cell Biol. 53, 164-172) with high purity and yield. Then the organelles are subjected to osmotic swelling. Since trichocysts then easily 'decondense' and entangle membranes, these cannot be isolated directly by centrifugation, but only by passage through a filter and subsequent centrifugation. Purity of membrane fractions is analysed by electron microscopy and SDS-PAGE, combined with silver staining or, after biotinylation, by avidin-peroxidase labelling. Molecular masses resolved in our gels are in a range from less than or equal to 15 to greater than or equal to 105 kDa. Main bands obtained with nd9-28 degrees C trichocyst membranes (most bands also being common to wild type trichocysts) are of about 16.5, 19-21, 27-29, 33-34, 44-45 (strong), 47-48 (strong), 57, 61, 65 (strong), 68-71, 75, 81, 94-95 (strong), 104 and greater than or equal to 110 kDa, from a total of approx. 23 bands resolved. There is no remarkable occurrence of dominant protein bands from trichocyst contents ('trichynins'), though these might represent up to 10(3)-times more of the total trichocyst proteins. The ratio of phospholipid/protein is approx. 0.2 mg/mg. The methodology developed might also be valuable for the isolation of extrusome membranes from some other protozoan species.

Alkaline phosphatase from Paramecium cilia and cell bodies: purification and characterization

A soluble alkaline phosphatase was purified 10 000-fold in an overall yield of 8% from both of the cilia and cell bodies of the protozoan Paramecium tetraurelia. The concentration in cilia (1.7 microM) was 6-fold higher than in cell bodies, although the latter contained most of the activity due to their much greater volume. The purified protein showed a single (36 kDa) protein staining band on SDS-PAGE. This value, in conjunction with the apparent molecular mass of 66 kDa for the native enzyme (gel filtration) suggests a dimeric structure. The specific activity of the purified phosphatase ranged from 10 to 70 mumols.min-1.mg-1 at the pH-optimum of 8.0 and the Km for p-nitrophenyl phosphate was 81 microM. Basal enzyme activity was inhibited by metal chelators and stimulated up to 12-fold by addition of divalent cations. Mg2+ acted as a non-essential mixed-type activator with a half-maximal effect at 7 microM. Ca2+ was inhibitory, the extent of inhibition was dependent on the concentration of Mg2+ in the assay. Furthermore, the kinetics of inhibition by Ca2+ varied with the Mg2+ concentration. Phosphate, pyrophosphate, and SH-group blocking agents also strongly inhibited. The enzyme did not dephosphorylate Tyr- or Ser-/Thr-phosphoproteins. The Paramecium enzyme is not of lysosomal origin and its properties are quite different from all known phosphatases. It is a novel type of phosphatase since it (i) shows F(-)-inhibition like Ser/Thr-phosphatases but (ii) is inhibited by vanadate and molybdate like Tyr-phosphatases, and (iii) inhibition by Ca2+ has not been reported for any other phosphatase.

Divalent cation-dependent ATPase activities in ciliary membranes and other surface structures in Paramecium tetraurelia: comparative in vitro studies

Cilia membrane preparations from axenically grown Paramecium contain ATPase activities with distinct electrophoretic mobilities on Triton-polyacrylamide gels [M.J. Doughty and E.S. Kaneshiro (1983) J. Protozool. 30, 569-575]. Such gel analyses also show additional ATPase activity bands associated with ciliary axonemes (dyneins), cell pellicles, exocytotic trichocysts, and the external cell surface (ectoenzyme). In the present report, the in vitro properties of these activities in various cell fractions were compared. The activity in ciliary membranes was stimulated by Ca2+ greater than Mg2+, in pellicles by Ca2+ greater than Mg2+, and in trichocysts by Ca2+ = Mg2+. The ecto-ATPase was strictly Ca2+ dependent. Determination of the affinities for various phosphate-containing substrates showed that the activities in all fractions were nucleoside triphosphate phosphohydrolases. Unlike the axonemal dynein ATPases, all other fractions were vanadate- and p-chloromercuribenzoate-insensitive. Activities in all cell fractions were sensitive to ruthenium red, the ciliary membrane being the most sensitive (Ki = 4 microM). The ciliary membrane Ca2+ ATPase activity exhibited an apparent affinity for CaATP2- of 9 microM and was inhibited by other divalent cations, La3+, and phosphate, but not by ADP or AMP. The kinetic properties of the ciliary membrane Ca2+ ATPase activity in wild type and several behavioral mutants were similar except for those in the pawn mutant, d495, and the paranoiac mutant, d490, both of which had lower specific activities. These studies support the finding that the ciliary membrane ATPase activity of Paramecium is a specific Ca2+-dependent ATPase distinct from other divalent cation-dependent ATPase activities found in either the cilia or other cell surface structures.