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.     

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.     

Multiple Hydrolases in Bean Leaves (Phaseolus vulgaris L.) and the Effect of the Halo Blight Disease Caused by Pseudomonas phaseolicola (Burkh.) Dowson

Multiple forms of hydrolytic enzymes were demonstrated in extracts of healthy bean leaves (Phascolus vulgaris L.) and bean leaves infected with the halo blight organism [Pseudomonas phaseolicola (Burkh.) Dowson] by polyacrylamide disc electrophoresis.Bean leaves contained up to 4 acid phosphatase bands, 9 esterase bands active towards alpha-naphthyl acetate, and 7 esterase bands towards alpha-naphthyl butyrate. Only low or no activity was found for alkaline phosphatase, lipase, and aminopeptidase.Two artifacts are described which were observed with the lead phosphate method for acid phosphatase and the Tween method for demonstration of lipase.After infection with the halo blight organism the major acid phosphatase of the host increased during early and decreased at later infection stages. An acid phosphatase of bacterial origin with a more neutral pH optimum could be demonstrated in infected leaves. It is suggested that the bacterial acid phosphatase plays a role in uptake of metabolites by the pathogen.Several esterase bands decreased after infection. One host band with activity towards alpha-naphthyl butyrate increased. Also the pathogen showed an esterase band with high activity towards alpha-naphthyl butyrate.     

A Permian nurse log and evidence for facilitation in high‐latitude Glossopteris forests

The biology of trees that grew in high‐latitude forests during warmer geological periods is of major interest in understanding past and future ecosystem dynamics. As we study the different plants that composed these forests, it becomes possible to make comparisons with ecosystem processes that occur today. Here we describe a silicified late Permian (Lopingian) glossopterid (seed fern) trunk from Skaar Ridge, central Transantarctic Mountains, Antarctica, with evidence of glossopterid rootlets growing into its wood. The specimen is interpreted as a nurse log similar to those seen in some extant forests. Together with evidence of glossopterid roots growing within the lacunae of older roots, this new specimen suggests the existence of facilitative interactions among the glossopterid trees that dominated the high‐latitude forests of Gondwana during the late Permian. More generally, the existence of self‐facilitation might have favoured the expansion of glossopterids within various environments, especially those at high palaeolatitudes, during the Permian icehouse to greenhouse transition.