Combined Action of Inhibitors of S-Adenosylmethionine Decarboxylase with an Antimalarial Drug, Chloroquine, on Plasmodium falciparum

ABSTRACT. Methylglyoxal bis (guanylhydrazone), (MGBG) a potent competitive inhibitor of S-adenosyl-L-methionine decarboxylase activity, Berenil, a trypanocidal agent and chloroquine, the commonly used antimalarial resulted in a dose dependent inhibition of Plasmodium falciparum in vitro. The IC₅₀ values of MGBG, Berenil and chloroquine were 224 μM, 40 μM and 42 nM respectively. Parasites treated with different concentrations of MGBG or Berenil were arrested at the trophozoite stage of the erythrocytic cycle. The combined action of chloroquine (10 nM) with either Berenil (0.1 mM) or MGBG (0.1 mM) on P. falciparum growth showed an additive inhibitory effect. The effect of these inhibitors alone and in combination on polyamine biosynthesis is also reported.     

Isozyme Specificity to Temperature

TEMPERATURE treatment of styles leads to self-compatibility in otherwise self-incompatible species of Oenothera^2,3, Lilium⁴ and Trifolium^5,6. I have studied the temperature treatment of esterase in styles of several species and hybrids of Lilium by using gel electrophoresis.     

Cation-impermeable Inside-out and Right-side-out Vesicles from Human Erythrocyte Membranes

The two surfaces of a membrane can be compared by isolating sealed vesicles which bare one side or the other to impermeable probe molecules. For this purpose, inside-out (IO) and right-side-out (RO) vesicles have been generated from human red blood cell membrane ghosts and partially resolved on dextran density gradients¹. We now report further characterization of this system, showing (a) that vesicles can be made which are impermeable to small solutes, including Na⁺ and K⁺, even though the parent ghosts are quite unsealed; (b) that the dextran gradient fractionation serves to separate sealed vesicles (which happened to be IO and RO, respectively, in the original study¹); (c) that impermeable RO vesicles form instead of IO vesicles if the published protocol is modified by the untimely addition of trace divalent cations; and (d) that the vesicle fractions can and must be accurately monitored for sealing and orientation to avoid misinterpretations such as those encountered in a previous sidedness study².     

Over-expression of STP13, a hexose transporter, improves plant growth and nitrogen use in Arabidopsis thaliana seedlings

In Arabidopsis thaliana , the regulation of hexose levels by the large monosaccharide transporter (MST) gene family influences many aspects of plant growth. The cloning and transgenic expression of one family member (STP13) enabled the manipulation of carbon (C) and nitrogen (N) metabolism in Arabidopsis . Transgenic seedlings constitutively over-expressing STP13 (STP13OX) had increased rates of glucose uptake, higher endogenous sucrose levels and accumulated more total C and biomass per plant when grown on soil-less media supplemented with 55 m m glucose and sufficient N (9 m m nitrate). Furthermore, STP13OX seedlings acquired 90% more total N than the Col-0 seedlings, and had higher levels of expression of the nitrate transporter NRT2.2 . In addition, STP13OX seedlings were larger and had higher biomass than Col-0 seedlings when grown under a limiting N condition (3 m m nitrate). Transgene analysis of STP13 reveals that its gene product is localized to the plasma membrane (PM) in tobacco BY-2 suspension cells, that it encodes a functional MST in planta , and that the STP13 promoter directs GUS expression to the vasculature and to leaf mesophyll cells. This work highlights the link between C and N metabolism, demonstrating that a plant's N use may be improved by increasing the availability of C.