Studies on lens regeneration inXenopus laevis

Zusammenfassung Es wurde die Regeneration der Augenlinse erwachsenerXenopus laevis nachuntersucht. Eine vollständige Entfernung der Linse gelang in wenigen Fällen. Die Neuentwicklung der Linse wurde nur von Linsenepithelresten, die nach der Lentektomie in der Kapsel zurückgeblieben waren, induziert.     

Constructive empiricism, observability and three kinds of ontological commitment

In this paper, I argue that, contrary to the constructive empiricist’s position, observability is not an adequate criterion as a guide to ontological commitment in science. My argument has two parts. First, I argue that the constructive empiricist’s choice of observability as a criterion for ontological commitment is based on the assumption that belief in the existence of unobservable entities is unreasonable because belief in the existence of an entity can only be vindicated by its observation. Second, I argue that the kind of ontological commitment that is under consideration when accepting a scientific theory is commitment to what I call theoretical kinds and that observation can vindicate commitment to kinds only in exceptional cases.     

Effect of plant lectins on Ustilago maydis in vitro

Ustilago maydis is an edible parasitic basidiomycete, which specifically infects corn (Zea mays) and teocintle (Z. diploperennis). To characterise the interaction between the basidiomycete and its host organism, we tested the effect of plant lectins with well-known sugar specificity on the growth and germination of U. maydis spores. Lectins specific for N-acetyl-D-galactosamine, such as those from Dolichos biflorus and Phaseolus lunatus, and the wheatgerm agglutinin specific for N-acetyl-D-glucosamine inhibited spore germination, but were ineffective in modifying U. maydis cell growth. The galactose-specific lectin from the corn coleoptyle inhibited both germination and cell growth, while the lectin concanavalin A (mannose/glucose specific) activated spore germination and growth. Our results suggest that specific saccharide-containing receptors participate in regulating the growth and maturation of U. maydis spores.     

Effects of plant lectins on cellular defense reactions of ascidian hemocytes

The effects of plant lectins on the three cellular defense reactions of hemocytes of the solitary ascidian,Halocynthia roretzi (hemocyte aggregation, phagocytosis, and an allogenic reaction), were investigated. Concanavalin A inhibited aggregation, while wheat germ agglutinin and ricin inhibited the allogenic reaction. Neither of the lectins showed inhibitory effects on phagocytosis, but ricin promoted phagocytosis. These effects of the lectins were diminished by the addition of sugars specific for the respective lectins. These results strongly suggest that different surface carbohydrates are involved in the recognition mechanisms of threeH. roretzi cellular defense reactions.     

The effect of tolbutamide on early embryos ofXenopus laevis

Summary The effect of tolbutamide on the early development of Xenopus laevis has been studied. The results suggest that continuous exposure to 3×10^–4 M tolbutamide causes abnormal development.Acknowledgments. I wish to thank Mr F. Schaefer who prepared the histological material, and Hoechst U.K. Ltd for their gift of tolbutamide.     

Effect of lectins from leguminous seeds on rat duodenal enterokinase activity

Summary Enterokinase activity from rat duodenal brush borders was assayed in vitro in the presence of purified lectins from 3 leguminous seeds. Noncompetitive inhibition of the enzyme was observed in each case.Phaseolus hemagglutinin was the most potent inhibitor among the 3 lectins tested.     

Identification of a catecholamine in the skin of the toad,Xenopus laevis,and the relation to the physiological melanophore reaction

Zusammenfassung Mit Hilfe chemischer und histochemischer Technik gelingt in der Haut vonXenopus laevis der Nachweis eines dopamingefüllten Reservoirs. Das Catecholamin ist mit der physiologischen Melanophorenreaktion verbunden.

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The authors are indebted to Prof. J. C. van deKamer for his encouragement and interest in these studies.     

Inhibition of the reinitiation of meiosis in Xenopus laevis oocytes by three natural antiproteases: antipain, chymostatin, and leupeptin]

Oocytes incubated for 1 hr. in saline containing 1 mg/ml of antipain, leupeptin or chymostatin do not reinstate meiosis when progesterone or ionophore A 23187 are added. On the contrary such oocytes remain able to undergo meiosis when injected with cytoplasm of maturing oocytes (MPF), with Rabbit phosphorylase kinase or with Beef protein kinase. These results demonstrate that the loss of responsiveness to progesterone or ionophore is not due to toxic effects but rather to some interference with a key event which occurs prior to MPF action.     

Effect of interrupting retino-hypothalamic connections on the melanophore response inXenopus laevis

Résumé On a estimé possible que les axones rétinohypothalamiques décrits chez certains amphibiens jouent un rôle dans le contrôle neuro-endocrinien de la pars intermedia de l'hypophyse. Mais si on sectionne chez desXenopus cette voie supposée, ces animaux peuvent néanmoins modifier la couleur de leur peau lorsqu'on les place sur les terrains différents. Il n'est donc pas vraisemblable que ces connections fassent partie d'un arc réflexe contrôlant la sécrétion de l'hormone mélanotrophique.     

Studies on the fungal phytotoxin victorin: Structures of three novel amino acids from the acid hydrolyzate

Summary The host-selective phytotoxin victorin, produced by the fungusCochliobolus victoriae, was found to be at least partially peptidic in nature, and did not contain victoxinine. The exact mass of the M-H ion was measured by FABMS as 795.1877. Derivatives of three major acid hydrolysis products were isolated. The structures of the corresponding amino acids were assigned as 2S,3R-3-hydroxyleucine, 5,5-dichloroleucine, and 3-hydroxylysine. A into victorin by the fungus in vivo.     

Purification and partial characterization of two lectins fromMomordica charantia

Summary 2 different lectins have been purified from the seeds ofMomordica charantia by gel-filtration and ion-exchange chromatography. These 2 lectins appear to be composed of 2 subunits of 26,000 daltons. Protein fraction I, but not II, showed agglutinating activity toward human type-O red blood cells. The amino acid compositions and amino-terminal sequences of these two homologous proteins are quite different.Acknowledgment. The skillful assistance of Ms M. Diane Forde is greatly acknowledged. Part of this work was supported by NIH grants CA18621 and AI09810 when the author was at Mount Sinai School of Medicine.     

Sex linkage of malic enzyme inXenopus laevis

Genetic analysis of mME variants (mitochondrial malic enzyme, E.C. 1.1.1.40) inXenopus laevis revealed sex linkage of the mMe locus and indicated a WZ/ZZ type of sex determination. Codominant mMe alleles occur on both W and Z chromosomes, with a recombination frequency of 6.1%±1.5% between mMe and the sex-determining locus (or region).     

Munological activity of transplanted spleens inXenopus laevis

Resumé Des rates immunisées deXenopus laevis qu'on greffe dans des hôtes qui les acceptent, peuvent y produire des réactions immunologiques. Ces réactions se dirigent ou contre l'hôte ou contre des gretfes épidermiques, prises à un troisième animal que l'hóte tolère. Au cours de ces réactions de greffe-coutre-hôte, la rate se trouve parfois attaquée.     

Sex linkage of malic enzyme in Xenopus laevis

Genetic analysis of mME variants (mitochondrial malic enzyme, E.C. 1.1.1.40) in Xenopus laevis revealed sex linkage of the mMe locus and indicated a WZ/ZZ type of sex determination. Codominant mMe alleles occur on both W and Z chromosomes, with a recombination frequency of 6.1% +/- 1.5% between mMe and the sex-determining locus (or region).