Two new species of Rhynchospora section Psilocarya (Cyperaceae)

Two new species ofRhynchospora sectionPsilocarya are described and illustrated.Rhynchospora eburnea is known from Amazonian Venezuela and nearby Brazil whileRhynchospora waspamensis is known only from eastern Zelaya, Nicaragua. These species are distinguished from most of the species of sectionPsilocarya by means of a key to the species found in the Americas south to and including the Amazon Basin.     

The role of edges in the selection of a jump target in Mantis religiosa

Before jumping to a landing object, praying mantids determine the distance, using information obtained from retinal image motion resulting from horizontal peering movements. The present study investigates the peering-jump behaviour of Mantis religiosa larvae with regard to jump targets differing in shape and size. The experimental animals were presented with square, triangular and round target objects with visual extensions of 20 degrees and 40 degrees. The cardboard objects, presented against a uniform white background, were solid black or shaded with a gradation from white to black. It was found that larger objects were preferred to smaller ones as jump targets, and that the square and triangle were preferred to the round disk. When two objects were presented, no preference was exhibited between square and triangular objects. However, when three objects were presented, the square was preferred. For targets with a visual angle of 40 degrees, the amplitude and velocity of the horizontal peering movements were greater for the round disk than for the square or triangle. This amplification of the peering movements suggests that weaker motion signals are generated in the case of curved edges. This may help to account for the preference for the square and triangle as jump targets.     

An antibody specific for coagulation factor IX enhances the activity of the intrinsic factor X-activating complex

During hemostasis the zymogen factor X (FX) is converted into its enzymatically active form factor Xa by the intrinsic FX-activating complex. This complex consists of the protease factor IXa (FIXa) that assembles, together with its cofactor, factor VIIIa, on a phospholipid surface. We have studied the functional properties of a FIXa-specific monoclonal antibody, 224AE3, which has the potential to enhance intrinsic FX activation. Binding of the antibody to FIXa improved the catalytic properties of the intrinsic FX-activating complex in two ways: (i) factor VIIIa bound to the FIXa-antibody complex with a more than 18-fold higher affinity than to FIXa, and (ii) the turnover number (kcat) of the enzyme complex increased 2- to 3-fold whereas the Km for FX remained unaffected. The ability of 224AE3 to increase the FXa-generation potential (called the "booster effect") was confirmed in factor VIII (FVIII)-depleted plasma, which was supplemented with different amounts of recombinant FVIII. In the presence of antibody 224AE3 the coagulant activity was increased 2-fold at physiological FVIII concentration and up to 15-fold at low FVIII concentrations. The booster effect that we describe demonstrates the ability of antibodies to function as an additional cofactor in an enzymatic reaction and might open up a new principle for improving the treatment of hemophilia.