Experimental infections of simians with human malaria: attempts to infect Callithrix penicillata with Plasmodium falciparum

After reviewing the use of non-human primates of the Old and New Worlds for human malaria research, we concluded that another experimental animal which is easily available to use and possible to rear indoors is needed. Thus, we studied the susceptibility of the marmoset Callithrix penicillata to Plasmodium falciparum erythrocytic infections. The marmosets received various P. falciparum human isolates, directly from a patient and from continuous cultures. The Palo Alto strain, which has been adapted to the night monkey Aotus trivirgatus and further maintained in the squirrel monkey Saimiri sciureus was also used. In a total of 20 marmosets we performed 31 inoculations, with 10(5) to 10(9) parasites, intraperitoneally, intracardiacly or intravenously. Blood samples from each animal were examined daily up to day 90 post-inoculation. None of the intact marmosets developed patent infections. Four out of 19 C. penicillata, previously splenectomized, showed circulating parasites for up to five days after intravenous inoculation with the Palo Alto strain, becoming negative thereafter. Neither the addition to the simian diet of p-aminobenzoic acid, essential for the parasite metabolism, nor drug-immunosuppression, improved the marmoset susceptibility to P. falciparum.     

Continuous culture of a recombinantEscherichia coli and plasmid maintenance for tryptophan production

Summary Production of tryptophan by a temperature sensitive recombinant microorganism (Escherichia coli W3110 trpLDtrpR ^ts tna ^– (pCRT185)) was investigated. In a single-stage continous culture, at an elevated temperature, 42°C (derepressed condition), tryptophan concentration increased in an early phase of the fermentation, and then gradually decreased with time. The reduction in the production rate was mostly due to the segregation of the plasmid and subsequent increase of plasmid-free cells. However, the plasmid could be maintained stable at 37°C, with repressed condition oftrp-operon, over 200 generations. A two-stage continuous culture system, i.e. cell growth was maintained in the first stage at 37°C and gene expression was induced in the second stage at 42°C, was therefore tested to improve the performance of the fermentation system. Operation of the two-stage system showed that the plasmid stability was significantly improved, and the specific rate of tryptophan production was maintained almost constant for more than 500 hours in the second stage.     

Novel stabilization of phenylalanine ammonia-lyase catalyst during bioconversion of trans-cinnamic acid to l-phenylalanine

Summary Production of l-phenylalanine from trans-cinnamic acid using isolate SPA10 cells was reduced to 26% of that observed initially when cells were reacted a second time with fresh substrate mixture. The stability (reuseability) of Phenylalanine Ammonia-Lyase (PAL) containing cells was significantly influenced by both the trans-cinnamate concentration and initial reaction pH. Using 2% t-cinnamate, l-phenylalanine production was 7-fold greater after 3 successive runs at pH 9.0 than at the optimum of pH 10.2. Cells reacted in the presence of 5% t-cinnamate were relatively unstable. Permeabilising agents, such as toluene and xylene, stimulated l-phenylalanine production but also enhanced instability of the catalyst. Several effectors were shown to stimulate the initial rate of the PAL bioconversion, but only sorbitol, alginate, glutaraldehyde, polyethylene glycol and glycerol conferred any significant degree of stability. Sparging of cultures and bioreactors with various gases revealed that oxygen enhanced PAL inactivation, CO₂ had little effect and nitrogen conferred remarkable stability on PAL activity for several weeks in culture medium. The presence of chloride ions (from HCl) and aeration of substrate mixtures resulted in poor reuseability of catalyst. A combination of H₂SO₄ substitution for HCl and N₂-sparging resulted in excellent initial conversions and good catalyst stability at 26°C but less at 30°C. The inclusion of 1.5 M sorbitol in reaction mixtures maintained PAL stability over several successive incubations.     

Recent advances in chemiluminescence-based immunoassays for steroid hormones

Several formats of solid-phase separation techniques for the measurement of steroids and urinary steroid conjugates using chemiluminescence as an end point are described. These formats include: (1) immunoadsorption of second antibodies directed against the first antibody on solid support; (2) specific immunoadsorbents consisting of primary antibodies covalently coupled to polymer beads; (3) second antibody coupled to a polymer containing magnetic particles. In these assays a steroid-chemiluminescent marker conjugate serves as the labelled ligand, and highly specific homologous monoclonal antibodies are used to provide optimal specificity and rigorous standardization. These techniques enabled the direct measurement of steroid glucuronides in diluted urine and of steroids in plasma.     

Effect of bacterial growth-inhibiting ingredients on the Ames mutagenicity of medicinal herbs

A solvent fractionation method was introduced to screen for mutagenicity in 10 medicinal herbs being consumed in Korea. The Ames mutagenicity test result of Scutellariae and Rhei was significantly increased by eliminating growth-inhibiting substances through solvent fractionation of the crude extract. It is suggested that a physicochemical pretreatment should reduce the false-negative results which are caused by the presence of growth-inhibiting substances in complex mixtures.     

Characterization of the Stimulation of Ethylene Production by Galactose in Tomato (Lycopersicon esculentum Mill.) Fruit

We have characterized the stimulation of ethylene production by galactose in tomatoes (Lycopersicon esculentum Mill.). The effect of concentration was studied by infiltrating 0, 4, 40, 100, 200, 400, or 800 micrograms galactose for each gram of fresh fruit weight into mature green `Rutgers' fruit. Both 400 and 800 micrograms per gram fresh weight consistently stimulated a transient increase in ethylene approximately 25 hours after infiltration; the lower concentrations did not. Carbon dioxide evolution of fruit infiltrated with 400 to 800 micrograms per gram fresh weight was greater than that of lower concentrations. The ripening mutants, rin and nor, also showed the transient increase in ethylene and elevated CO₂ evolution by 400 micrograms per gram fresh weight galactose. 1-Aminocyclopropane-1-carboxylic acid (ACC) content and ACC-synthase activity increased concurrently with ethylene production. However, galactose did not stimulate ACC-synthase activity in vitro. The infiltrated galactose in pericarp tissue was rapidly metabolized, decreasing to endogenous levels within 50 hours. Infiltrated galacturonic acid, dulcitol, and mannose stimulated transient increases in ethylene production similar to that of galactose. The following sugars produced no response: sucrose, fructose, glucose, rhamnose, arabinose, xylose, raffinose, lactose, and sorbitol.     

Effect of GA3 on the Cyclic AMP Biosynthesis in Maize Seedling

The effect of GA₃ on the biosynthesis of cAMP was studied toinvestigate the mechanism of gibberellic acid action. The presenceof cAMP in germinating maize seedlings was confirmed. The concentrationgradient of cAMP in maize seedlings inclined from shoot apexto root. The amount of cAMP in maize shoot was increased about3.3 times by exogenous GA₃. These results indicate that thebiosynthesis of cAMP is stimulated by GA₃. (Received June 17, 1986; Accepted January 22, 1987)     

Dynamics of populations with changing rates: generalization of the stable population theory

A general and complete exposition of the dynamics of populations with changing vital rates is given in the discrete time formulation. Results obtained are stronger than Lopez's or Hajnal's. In addition to the proof of existence of limits, an explicit expression for the age distribution is obtained by considering forward products of population projection matrices, while an explicit expression for the generalized reproductive values is obtained by considering backward products. The forward and backward characteristic equations respectively determine the forward and backward growth rates. The relative age distribution is compared to the alternative expression of Y.J. Kim (1986, Demography 23 (3), 451-461), which is the discrete version of S.H. Preston and A.J. Coale (1982, Pop. Index 48 (2), 217-259).     

Neural crest development in the Xenopus laevis embryo, studied by interspecific transplantation and scanning electron microscopy

The Xenopus borealis quinacrine marker and scanning electron microscopy have been used to study the appearance, migration, and homing of neural crest cells in the embryo of Xenopus. The analysis shows that the primordium of the neural crest develops from the nervous layer of the ectoderm and consists of three segments at early neurula stages. This primordium is located in the lateral halves of the neural folds behind the prospective eye vesicles. The histological and experimental evidence shows that the neural crest cells also originate from the medial portion of the neural folds. The neural crest segments in the cephalic region start to migrate just before the closure of the neural tube. Isotopic and isochronic unilateral grafts of X. borealis neural crest into X. laevis embryos were performed in order to map the fate of the cranial crest segments and the vagal-truncal neural crest. The analysis of the X. laevis host embryos shows that the mandibular crest segment contributes to the lower jaw (Meckel's cartilage), quadrate, and ethmoid-trabecular cartilages, as well as to the ganglionic and Schwann cells of the trigeminus nerve, the connective tissues, the mesenchymal and choroid layers of the eye, and the cornea. The hyoid crest segment is located in the ceratohyal cartilage and in ganglia VII and VIII. The branchial crest segment migrates from the caudal part of the otic vesicle and divides into two portions which contribute to the cartilages of the gills. The vagal-truncal neural crest starts to migrate later at stage 25. It migrates by means of the vagus complex in a ventral direction and penetrates into the splanchnic layer of the digestive tract. The trunk neural crest cells disperse into three different pathways which differ from those of the avian embryo at this level.