Restriction of PGK-B to spermatogenic cells: Evidence from experimentally cryptorchid mice

The hypothesis that PGK-B, like LDH-C₄, is restricted to spermatogenic cells was explored by examining isozyme patterns in testes from mice depleted of germinal cells by surgical cryptorchism. In experimentally cryptorchized C57BL/10Sn males, decline in PGK-B activity paralleled decline in LDH-C₄ activity and was correlated with degeneration of spermatocytes, spermatids, and spermatozoa. Trace amounts of these sperm isozymes found in cryptorchid testes after the depletion of maturing germ cells probably came from degenerated spermatids and spermatocytes and not from somatic testicular cells.     

CYTODYNAMICS IN THE THYMUS OF YOUNG ADULT MICE:

Cell proliferation and cell loss in the thymic blast cell population were studied in young adult mice by (1) stathmokinetic methods combined with an analysis of the PLMe-curve after a pulse ³H-TdR, and (2) nigrosin-dye exclusion combined with ³H-TdR-autoradiography. It was calculated that about 17% of the blast cells do not progress into mitosis within the period of an average cell cycle. The dye exclusion studies indicated a rate of blast cell death of about 2–5 %/hr. The two methods of assessing blast cell loss (death) support each other very well. In spite of these findings scintillation countings on thymuses removed from 1 to 17 hr after ³H-TdR injection showed fairly constant levels of thymic radioactivity. This suggests a very extensive reutilization of ³H-labelled break-down products from dying blast cells. The very sparse labelling of pyknotic thymocytes strongly suggests that thymic blast cells do not become pyknotic. The rate of small thymocyte production and disappearance was studied by pulse and repeated ³H-TdR labelling techniques combined with dye exclusion studies and pyknotic counts. The data from the repeated labelling experiment were analysed by use of a model based on the assumption of first order kinetics of small viable, dead, and pyknotic thymocytes. The rate of cell production was estimated to 1–6 %/hr whereas the rates of cell loss due to disintegration, i.e. supravital stainability and nuclear pyknosis, were calculated to 0–02 %/hr and 0–0006 %/hr respectively. Cell loss due to disintegration was less than 2 % of the total loss of small thymocytes. It was concluded that pyknotic counts are a useless method of assessing the cell death in the population of thymic blast cells and small thymocytes. On the basis of a model for thymocyte proliferation, production and loss it is suggested that about 45 % of the small viable thymocytes re-enter the generative cell pool, whereas about 55% disappear by emigration.     

Uptake and Elimination of Poliovirus by West Coast Oysters

Accumulation of poliovirus Lsc-2ab by West Coast oysters was determined by using a stationary seawater system, and depuration was determined by using both stationary and free-flow systems. Results indicate that these shellfish have the same pattern of accumulation and localization of viruses as do East Coast species. However, uptake appeared to occur more rapidly than described for East Coast shellfish. There appeared to be a gradual diffusion of virus from the digestive area into the body. Depuration was found to occur more rapidly and completely under free-flow conditions than in a stationary system.     

Chinning by maleTupaia belangeri: The effects of scent marks of conspecifics and of other species

Journal of Comparative Physiology A -     

Isoproterenol inhibition of horse serum cholinesterase is connected with subunit dissociation

Tetrameric cholinesterase from horse serum undergoes concentration-dependent dissociation. The dimer is highly stable so that even on SDS polyacrylamide gels subunit dissociation to the 80-kDa polypeptide chains is incomplete. Glutaraldehyde cross-linking confirms this finding, giving rise to a tetramer: dimer ratio of approximately 1:1. The beta-adrenergic agent isoproterenol acts as an inhibitor of the enzyme with respect to butyrylthiocholine hydrolysis; inhibition kinetics point to a dissociative effect of the ligand as the underlying mechanism (S?ylemez, Z. & Ozer, I. (1985) Comp. Biochem. Physiol. 81c, 433-437). Evidence from sedimentation analysis confirms this hypothetical mechanism: the sedimentation coefficient in the presence of saturating concentrations of both the substrate butyrylthiocholine and the inhibitor isoproterenol shows a 35 +/- 5% decrease; in high speed sedimentation equilibria the weight average molecular mass is shifted from the tetramer (Mr = 312 +/- 12 kDa) to the dimer (Mr = 160 +/- 10 kDa). The transition is complete at isoproterenol concentrations below saturation. Applying glutaraldehyde cross-linking to monitor the particle distribution at varying isoproterenol concentrations confirms the change in quaternary structure in a qualitative way. Enzyme concentrations applied in the present experiments are in the range of the concentration of cholinesterase in horse serum. Therefore the dissociative mechanism of isoproterenol on the enzyme may be of biological significance.     

EpCAM: Structure and function in health and disease

Injection of tumor cells in mice more than 30 years ago resulted in the discovery of an epithelial antigen, later defined as a cell adhesion molecule (EpCAM). Although EpCAM has since evoked significant interest as a target in cancer therapy, mechanistic insights on the functions of this glycoprotein have been emerging only very recently. This may have been caused by the multitude of functions attributed to the glycoprotein, its localization at different subcellular sites and complex posttranslational modifications. Here, we review how EpCAM modifies cell–cell contact adhesion strength and tissue plasticity, and how it regulates cell proliferation and differentiation. Major knowledge derived from human diseases will be highlighted: Mutant EpCAM that is absent from the cell surface leads to fatal intestinal abnormalities (congenital tufting enteropathy). EpCAM-mediated cell proliferation in cancer may result from signaling (i) via regulated intramembrane proteolysis and/or (ii) the localization and association with binding partners in specialized membrane microdomains. New insight in EpCAM signaling will help to develop optimized cancer therapies and open new avenues in the field of regenerative medicine.     

Interaction of cibacron blue 3G-A and related dyes with nucleotide-requiring enzymes

Cibacron Blue 3G-A (I), the chromophore in Blue Dextran, its structural isomer Cibacron Brilliant Blue BR-P (II), and two other structural analogs (III, IV) were used to probe the nucleotide binding sites of selected kinases and dehydrogenases. Inhibition studies indicate that the portion of the dye molecule necessary for effective inhibition of nucleotide binding is a structure similar to 1-amino-4(4′-aminophenylamino)-anthraquinone-2,3′-disulfonic acid (ASSO; III). The strong inhibition exhibited by these dyes is likely to be due to interaction with specific nucleotide binding sites, irrespective of the presence of a “dinucleotide fold” in the proteins' supersecondary structure.     

Die Protochlorophyll(ID)-Umwandlung und Ihre Beziehungen zur Photooxydation der Ascorbinsäure bei Etiolierten Keimpflanzen

Zusammenfassung Bei etiolierten Keimpflanzen von Triticum vulgare wurden die vom protochlorophyll(id) zum Chlorophyll führenden Syntheseschritte untersucht.Dabei zeigte sich, daß die Chlorophyllsynthese, zumindest vor der Lag-Phase, nicht nur den Weg über das Chlorophyllid nimmt, sondern auch über Protochlorophyll erfolgen kann, wobei allerdings etwa 90% des gebildeten Chlorophylls durch Protochlorophyllid-Reduktionen entstehen.Von diesem Pigment werden 76–88% photoreduziert, vom Protochlorophyll hingegen nur etwa 40–70%.Was die Frage des Wasserstoffdonators für diese Photoreduktion anbetrifft, so haben die vorliegenden Untersuchungen ergeben, daß im Rotlicht stöchiometrische Beziehungen zwischen der Protochlorophyll(id)-Reduktion und der Photooxydation der AS bestehen. Dadurch wird der Gedanke nahegelegt, daß bei der in vivo stattfindenden Phototransformation des Protochlorophyll(id)-Holochroms die AS als Wasserstoffdonator eine Rolle spielt.Daraus ergibt sich für die Rolle der AS in den Chloroplasten eine neue Deutungsmöglichkeit.

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The protochlorophyll(ide) transformation and its relation to the photooxidation of ascorbic acid in etiolated seedlings

Summary The terminal steps in chlorophyll synthesis leading from protochlorophyll(ide) to chlorophyll have been investigated on etiolated seedlings of Triticum vulgare.It could be demonstrated that at least before the lag-phase the synthesis of chlorophyll proceeds not only via protochlorophyllide but also via protochlorophyll; however, about 90% of the synthesized chlorophyll originates from protochlorophyllide reduction.By a two-minute illumination with 7000 Lux 76–88% of the protochlorophyllide but only 30–60% of the protochlorophyll is transformed into chlorophyll(ide).As to the question of the hydrogen donor for this transformation, the present investigations have revealed that in red light the protochlorophyll(ide) reduction corresponds to the photooxidation of ascorbic acid. Hence it is suggested that in the photoreduction in vivo ascorbic acid could be involved as a reductant for the pigment. This supposition offers a new interpretation of the role of ascorbic acid in the chloroplasts.

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Im Text werden folgende Abkürzungen verwendet: AS=Ascorbinsäure, DAS=Dehydroascorbinsäure.