Yolk utilization inScyliorhinus canicula,an oviparous dogfish

Synopsis Using plastic embedding techniques and semithin sections, in order to overcome the difficult sectioning of yolky eggs, we have been able to carry out histological study of the external yolksac from fertilization until birth in the oviparous dogfishScyliorhinus canicula. The endoderm and its contacting giant yolk nuclei remained very flat, seemingly inactive, during the larger part of development. They became activated only when the external yolksac (EYS) began to shrink. This activation increased along a vegetal-animal gradient in the EYS, but it was essentially restricted to the parts located near the yolk stalk. A statistical study of oocyte, yolk, embryo and newborn fresh and dry weights confirmed that the mass of dry tissue in the embryo (30mg) and in EYS wall (<1 mg) at mid-development were still very low compared to 0.8–1.5 g mass of yolk available for development. This explains why yolk weight remained practically the same during the first half of development. The end of this first period was marked by entry into the pre-hatching state at 85–115 days under laboratory conditions (14–16°C). At this time, yolk began to enter the spiral gut, where it was digested during the second half of development and during one week period after eclosion. Eclosion occurred 170–220 days after egg laying or extraction from oviduct. Two internal storage organs were studied biometrically in the newborn: the internal yolksac (IYS), and the liver, which was fully developed at birth. Both IYS and liver dry weights corresponded to about 10% of the original yolk, while the gut was only 2%, and the rest of the newborn body 58%. Thus, about 20% of yolk dry mass was consumed during development, a figure that is low for oviparous animals.     

Uninfected red cells from malaria-infected blood: Alteration of fatty acid composition involving a serum protein: An in vivo and in vitro study

Summary Alteration of uninfected erythrocytes, fromPlasmodium (the malaria parasite)-infected blood remained an open question. In this study we compared the in vivo fatty acid compositions of control and uninfected monkey erythrocytes. A large (40%) increase in the linoleic acid level was observed, which was recovered mostly in neutral lipids. An in vitro system was developed to study medium-mediated alterations of cultured erythrocytes byPlasmodium falciparum. The increase in the linoleate level was reproduced in vitro and was also localized in the neutral lipid fraction, especially in triacylglycerols. Studies using proteolytic digestion and heat denaturation showed that a heat-labile serum protein is indispensable for the increase in the linoleate level of red cells treated with the supernatant, ofP. falciparum cultures. Both the function and the mechanism of this modification of uninfected erythrocytes still remain unknown. This work was supported by the UNDP/World Bank/WHO special program for Research and Training in Tropical Diseases (grant T16-181-M2-15B).     

Effect of Steam Sterilization and Gamma Irradiation of Peat on Quality of Rhizobium Inoculants

Data obtained by independent tests on each of 483 batches of Rhizobium inoculants for Glycine max, Medicago sativa, and Arachis hypogaea, manufactured commercially in South Africa, are reported and discussed. Whereas the average cell count per gram per batch was well in excess of 10⁹, inoculants for G. max and M. sativa manufactured with peat treated with gamma irradiation at a dose of 50 kGr contained significantly higher numbers of Rhizobium cells than inoculants from peat which received 25 kGr. Inoculants for M. sativa manufactured with steam-sterilized peat were similar in quality to those prepared with peat irradiated at a dose of 50 kGr. Contrary to the inoculants for G. max and M. sativa, the Rhizobium strain used in inoculants for A. hypogaea was apparently insensitive to the effect on peat of the higher gamma irradiation dosage.     

Bradavidin II from Bradyrhizobium japonicum: a new avidin-like biotin-binding protein

A gene encoding an avidin-like protein was discovered in the genome of B. japonicum. The gene was cloned to an expression vector and a protein, named bradavidin II, was produced in E. coli. Bradavidin II has an identity of 20-30% and a similarity of 30-40% with previously discovered bradavidin and other avidin-like proteins. It has biochemical characteristics close to those of avidin and streptavidin and binds biotin tightly. In contrast to other tetrameric avidin-like proteins studied to date, bradavidin II has no tryptophan analogous to the W110 in avidin (W120 in streptavidin), thought to be one of the most essential residues for tight biotin-binding. Homology modeling suggests that a proline residue may function analogously to tryptophan in this particular position. Structural elements of bradavidin II such as an interface residue pattern or biotin contact residues could be used as such or transferred to engineered avidin forms to improve or create new tools for biotechnological applications.     

Metabolomic and mass isotopomer analysis of liver gluconeogenesis and citric acid cycle. I. Interrelation between gluconeogenesis and cataplerosis; formation of methoxamates from aminooxyacetate and ketoacids

We conducted a study coupling metabolomics and mass isotopomer analysis of liver gluconeogenesis and citric acid cycle. Rat livers were perfused with lactate or pyruvate +/- aminooxyacetate or mercaptopicolinate in the presence of 40% enriched NaH(13)CO(3). Other livers were perfused with dimethyl [1,4-(13)C(2)]succinate +/- mercaptopicolinate. In this first of two companion articles, we show that a substantial fraction of gluconeogenic carbon leaves the liver as citric acid cycle intermediates, mostly alpha-ketoglutarate. The efflux of gluconeogenic carbon ranges from 10 to 200% of the rate of liver gluconeogenesis. This cataplerotic efflux of gluconeogenic carbon may contribute to renal gluconeogenesis in vivo. Multiple crossover analyses of concentrations of gluconeogenic intermediates and redox measurements expand previous reports on the regulation of gluconeogenesis and the effects of inhibitors. We also demonstrate the formation of adducts from the condensation, in the liver, of (i) aminooxyacetate with pyruvate, alpha-ketoglutarate, and oxaloacetate and (ii) mercaptopicolinate and pyruvate. These adducts may exert metabolic effects unrelated to their effect on gluconeogenesis.     

Carnivory and active hunting by the planktonic testate amoeba <Emphasis Type="Italic">Difflugia tuberspinifera</Emphasis>

Difflugia tuberspinifera, a testate amoeba found in the open water plankton of Liuxi He and other south Chinese reservoirs during summer, is one of six or more species that occasionally live a pelagic life. Here, we suggest that its incentive to leave the bottom might be the abundance of food in the water column rather than temperature. This Difflugia (and perhaps the other pelagic species as well) is indeed an actively hunting carnivore that catches small rotifers and other prey in the same size range. In Liuxi He, it readily feeds on Collotheca cf. mutabilis, which it catches and consumes with remarkable agility: it first inspects the jelly tube that protects the prey, then moves to the bottom of it, perforates the jelly near the prey’s foot, and finally ingests the rotifer foot-first.     

Incorporating dipolar solvents with variable density in Poisson-Boltzmann electrostatics

We describe a new way to calculate the electrostatic properties of macromolecules that goes beyond the classical Poisson-Boltzmann treatment with only a small extra CPU cost. The solvent region is no longer modeled as a homogeneous dielectric media but rather as an assembly of self-orienting interacting dipoles of variable density. The method effectively unifies both the Poisson-centric view and the Langevin Dipole model. The model results in a variable dielectric constant in the solvent region and also in a variable solvent density that depends on the nature of the closest exposed solute atoms. The model was calibrated using small molecules and ions solvation data with only two adjustable parameters, namely the size and dipolar moment of the solvent. Hydrophobicity scales derived from the solvent density profiles agree very well with independently derived hydrophobicity scales, both at the atomic or residue level. Dimerization interfaces in homodimeric proteins or lipid-binding regions in membrane proteins clearly appear as poorly solvated patches on the solute accessible surface. Comparison of the thermally averaged solvent density of this model with the one derived from molecular dynamics simulations shows qualitative agreement on a coarse-grained level. Because this calculation is much more rapid than that from molecular dynamics, applications of a density-profile-based solvation energy to the identification of the true structure among a set of decoys become computationally feasible. Various possible improvements of the model are discussed, as well as extensions of the formalism to treat mixtures of dipolar solvents of different sizes.