Uptake and Metabolism of L-Serine by Pneumocystis carinii carinii

ABSTRACT. Serine is an important amino acid that is utilized in the biosyntheses of proteins and lipids. It is directly incorporated into the head group of phosphatidylserine, which in turn can be converted to other phospholipids. Also, it is required for the formation of long chain bases, precursors of sphingolipids. Uptake and incorporation of radiolabeled serine into both lipids and acid-precipitable material were demonstrated in Pneumocystis carinii carinii organism preparations freshly isolated from infected rat lungs. Radioactivity in proteins was about double that observed in lipids. Liquid scintillation spectrometry of metabolically radiolabeled lipids separated by thin-layer chromatography showed 53% of the total radioactivity were in phosphatidylserine, 12% in phosphatidylethanolamine, 24% in ceramides, and 11% in long chain bases and other compounds. Four long chain bases were detected by thin-layer chromatography in hydrolyzed P. carinii ceramides metabolically labeled with radioactive serine. Phytosphingosine and dihydrosphingosine were tentatively identified by their migrations on thin-layer plates. Radiolabeled ethanolamine was incorporated into P. carinii phosphatidylethanolamine, but relatively low incorporation of radiolabeled choline into phosphatidylcholine occurred. The observations made in this study indicated that P. carinii has the biosynthetic capacity to metabolize phospholipid head groups and to de novo synthesize sphingolipids. L-Cycloserine and β-CI-D-alanine, inhibitors of long chain base synthesis, reduced the incorporation of serine into P. carinii long chain bases and ceramides, which supported the conclusion that the pathogen synthesizes sphingolipids.     

Membrane-Associated Polysaccharides Composition, Nutritional Requirements and Cell Differentiation in Herpetomonas roitmani: Influence of the Endosymbiont

Herpetomonas roitmani , a trypanosomatid containing a bacterial endosymbiont, was cured by high doses of chloramphenicol. Wild-type and cured flagellates were compared as to polysaccharide composition, nutritional requirements and cellular differentiation. Fucose (18.0%), xylose (15.7%), mannose (38.9%), galactose (10.8%), glucose (16.4%) and inositol (< 1.0%) were identified as polysaccharide components of cured H. roitmani as assessed by gas-liquid chromatography. However, the wild-type strain displayed a markedly different sugar profile, in that xylose was absent and inositol preferentially synthesized, whereas the other monosaccharide components remained unchanged. Variations in nutritional pattern also occurred between both strains. The bacterial endosymbiont seems to provide the flagellates with nutritional factors, including usual amino acids, vitamins, purine (as adenine) and hemin. The process of cell differentiation was also significantly influenced by the endosymbiont. Opisthomastigote forms predominate (72.0%) in cured as compared with wild-type H. roitmani (37.0%).     

High water roost selection by waders: maximizing feeding opportunities or avoiding predation?

During the highest spring tides the intertidal sediment flats of estuaries are fully inundated at high water, and waders have no choice but to move to supratidal roosts, e.g. on open farmland, saltpans or beaches. However, in many estuaries during the lowest neap or intermediate tides there are sectors of upper intertidal sediment flats that remain exposed even at the peak of high water, and so waders have the choice of roosting either there or in supratidal sites. In the Tagus Estuary, Portugal, as elsewhere, waders use both types of roosts during high water. Our main objective was to understand what makes waders opt for one of these two types of available roosts. We monitored wader use of saltpans and intertidal roosts from spring to neap tides, and measured foraging and alarm behaviour, prey availability and disturbance by predators. Most of the wader species studied chose intertidal (mudflat) roosts whenever these were available, and only roosted in saltpans during the peak of spring tides. We hypothesized that this preference was explained either by an attempt (i) to continue feeding into the high water period, or (ii) to minimize predation risk. Extending feeding time into the high water period did not seem to be very relevant for roost choice because both prey availability and foraging activity were low in both types of roosts. However, predator disturbance was several times higher in the saltpans than in the intertidal roosts, suggesting that this factor may be the determinant in the choice of roost type.     

Patterns of oviposition by Sandia xami (Lepidoptera, Lycaenidae) in relation to food plant apparency

ABSTRACT.

• 1 The butterfly Sandia xami (Reakirt) has a very clumped yearly pattern of oviposition on its food plant Echeveria gibbiflora D.C., and the mean number of eggs per plant is always very low.
• 2 Three features of host plants are highly associated with the probability of being oviposited upon: height of plant; degree of conspicuousness; and degree of isolation from conspecific plants.
• 3 The relative importance of these factors as predictors of the probability of oviposition change according to the time scale considered: height and conspicuousness are more important over short (weekly) time intervals whilst isolation takes precedence over longer (yearly) periods.
• 4 It is hypothesized that the clumped pattern of oviposition is responsible for the low numbers of the butterflies relative to their very abundant food plant.

     

Analysis of flavone-flavonol ratio in Dicotyledoneae

The flavone-flavolol ratio (fo/fl) for Dicotyledoneae is studied through graphic comparisons between indices indicative of morphological tendencies: the herbaceousness and Sporne indices. These comparisons show a tendency toward the reduction of flavone biosynthesis in arboreous and shrubby taxa. Ligneous families (HI ≤150.0) and morphologically more primitive families (SI ≤55) possess fo/fl <1.OO. However, the relationship between evolutionary status of families with fo/fl values is not simply linear in Dicotyledoneae, because more advanced families are also characterized by a wider range of variation in fo/fl values.     

EARLY EFFECT OF MOSQUITO LARVAE EXTRACT ON MOUSE CELLS PROLIFERATIONIN VIVO

It has been demonstrated that mosquito larvae crude extract has an inhibiting effect on the mitotic rate of several mouse cell populations. The sampling period was 16–24h after treatment, when mitotic peak normally occurs. The present paper reports the effect of mosquito larvae crude extract on the proliferation of hepatocytes, renocytes, Lieberkhün crypt enterocytes, and sialocytes. In this case, the sampling period covered the dark phase of the day, during the first 12h after treatment. Colchicine-arrested metaphases were controlled at 20/04, 00/08 and 04/12 (Time of Day/Time Post Injection). The mitotic rate was significantly increased in hepatocytes and renocytes and inhibited in duodenum enterocytes. In view of the time chosen to administer the treatments and the time elapsed until sampling, we conclude a probable effect of the extract at the G₂-M point of the cell cycle.     

Effect of Phosphatidylcholine on Acrosome Breakdown and Fertilizing Capacity of Amphibian Spermatozoa

The effect of vesicles of purified egg yolk phosphatidylcholine on the fertilizing capacity and acrosome breakdown of amphibian spermatozoa was studied. When Bufo arenarum spermatozoa were incubated with either small unilamellar vesicles (prepared by sonication) or with large unilamellar vesicles (prepared by reverse-phase evaporation) a decrease in the fertilizing capacity of spermatozoa was found. At the same phosphatidylcholine concentration, large unilamellar vesicles were more inhibitory than small unilamellar vesicles. The inhibition was dependent upon the phospholipid concentration and the length of the incubation period. Small unilamellar vesicles did not modify the time course of acrosome breakdown in Leptodactylus chaquensis , while large unilamellar vesicles markedly accelerated the rate of acrosome breakdown. In both biossays, the charge of the vesicles (made either positive or negative by the addition of 5% stearylamine or 5% phosphatidic acid) did not influence their biological effect. Multilamellar vesicles did not alter the fertilizing capacity nor the acrosome breakdown. We conclude that the size and the structure of the vesicles are important parameters in determining the inhibitory capacity of phosphatidyl choline on amphibian fertilization.