Irmentraut Löw

Interaction of actin with phalloidin:: Polymerization and stabilization of F-actin

The cyclic peptide phalloidin, one of the toxic components of Amanita phalloides prevented the drop of viscosity of F-actin solutions after the addition of 0.6 M KI and inhibited the ATP splitting of F-actin during sonic vibration. The data concerning ATP splitting are consistent with the assumption (a) that only 1 out of every 3 actin units of the filaments needs to be combined with phalloidin in order to suppress the contribution of these 3 actins to the ATPase activity of the filament and (b) that all actin units of the filaments can combine with phalloidin with a very high affinity. -halloidin did not only stabilize the actin-actin bonds in the F-actin structure but it also increased the rate of polymerization of G-actin to F-actin. The ability of F-actin to activate myosin ATPase was not affected by phalloidin. The tropomyosin-troponin complex did not prevent the stabilizing effect of phalloidin on the F-actin structure.

Stabilization of F-actin by phalloidin reversal of the destabilizing effect of cytochalasin B

The cyclic peptide phalloidin, a toxic component of the mushroom Amanita phalloides prevents the reduction by KI of the high viscosity of F-actin and inhibits the ATPase activity of F-actin during ultrasonic vibration [ 1 ] . Cytochalasin B (CB), a metabolite of the fungus Helminthosporium dematioideum, on the other hand obviously weakens the F-actin structure. This can be concluded from the fact that CB inhibits cellular functions that are believed to be linked to actin-like microfilaments (for reviews see [2] and [3 ] ) and that it decreases the visosity of F-actin [4] . This communication describes that phalloidin is able to antagonize the weakening effect, which CB exerts on F-actin structure.

DIE WIRKUNG EINIGER SOLANUM‐ALKAOIDGLYKOSIDE AUF DEN KARTOFFELKÄFER, LEPTINOTARSA DECEMLINEATA SAY1,2

Die kristallisierten Solanum‐Alkaloidglykoside (Solanin, Chaconin, Leptinin I, Leptinin II, Leptin I, Demissin und Tomatin) und ein amorphes Leptin III — Präparat wurden im Fraßtest an Kartoffelkäfem geprüft. Die Resistenz von Solanum “chacoense” gegen Leptinotursa kann durch den Gehalt an Leptinen erklärt werden. Die Leptine gehen unter Abspaltung der Acetylgruppe in die Leptinine über und verlieren darnit ihre hohe fraßabschreckende Wirksamkeit. DDT‐resistente Käfer sind gegen Solanum chacoense, die Leptine und die Leptinine unempfindlicher als normale.

The interaction of phalloidin. Some of its derivatives, and of other cyclic peptides with muscle actin as studied by viscosimetry.

Phalloidin (Ia), a component of the toxic green deathcap toadstool Amanita phalloides [ I] induces ir, vivo as well as in vitro the formation of filamentous structures in the cytoplasmic membrane fraction of (rat) liver as observed by electron microscopy [2]. The nature of these filaments as actin has been proven by their reaction with heavy meromyosin to give arrow head-like structures [3]. In contrast to F-actin, however, are the phalloidin-induced fibrils (Ph-filaments) resistant against 0.6 M KI. Consequently also F-actin from rabbit muscle was treated with the toxin and could so be transformed into a modified form (Ph-actin), which proved resistant against 0.6 M KI too. Ph-actin is also formed from G-actin by adding phalloidin to a solution of low ionic strength but sufficiently high ((0.7 mM) Mg2+ concentration. Since the process of polymerization of G-actin to F-actin (Phactin) can be followed more easily by viscosimetry we studied the interaction of G-actin with phalloidin (Ia), phallacidin (Ib), desmethylphalloin (Ic), its toxic and non-toxic sulfoxides (Id, Ie), the non-toxic derivatives desthiophalloidin (If) and secophalloidin (Ig) as well as a-amanitin and a soluble preparation of antamanide. Further the inhibiting effect of cytochalasin B (CB) on the formation of Ph-actin was investigated.

Interaction between rabbit muscle actin and several chaetoglobosins or cytochalasins.

Abstract The mold metabolites chaetoglobosins Ch-A, B, C, E, F, and J exert, as do the cytochalasins CB, CD, CE, and CG, enhancing effects of various strength on the polymerization of rabbit muscle G-actin. The polymers formed differ widely in their viscosity, Ch-B and Ch-J leading to the least viscous actins. Equal states of viscosity are arrived at by interaction of F-actin with the respective drugs. There is no correlation between the ATP hydrolyzing activity of F-actin elicited by the various cytochalasins and their influence on the viscosity.

Dual effect of Ca2+ on ultrasonic ATPase activity and polymerization of muscle actin

Millimolar concentrations of Ca2+ stimulate actin polymerization whereas micromolar concentrations of Ca2+ depress polymerization. This latter effect leads to a reduction of ATPase (ATP phosphohydrolase, EC 3.6.1.3) activity of actin during sonication at low Mg2+ concentrations and in the absence of KCl. In the presence of KCl (90 mM) there is activation of ATPase activity by micromolar Ca2+ concentrations. These Ca2+ effects are half-maximal at a Ca2+ concentration of 2-10(-7) M. They can be explained by assuming that that ATPase activity is optimal in a medium range of actin polymer stability and that micromolar Ca2+ concentrations tend to labilize and depolymerize F-actin.

Über die protoäscigeninester aus äscin

Abstract Acid hydrolysis of escin yields protoescigenin-21-tiglic acid (angelic acid) ester, protoescigenin-28-tiglic acid (angelic acid) ester and 16-acetyl-protoescigenin.

Prevention by aging or by cytochalasin B of phalloidin stimulated formation of microfilaments in cell membrane preparations of rat liver

SummaryThe increased occurrence of microfilaments in cell membrane preparations of rat liver poisoned with phalloidin in vitro was shown to be dependent on the age of the preparations. Cytochalasin B inhibits the formation of microfilaments stimulated by pahlloidin.

Zur retreo-diels-alder-reaktion pentacyclischer triterpene unter elektronenbeschuss: Protoäscigenn und verwandte verbindungen

Abstract If at least one of the hydroxyl groups attached to ring D or E of protoescigenins is substituted, then the moiety at C-16 will be eliminated in the form of water, acetic acid or acetone before the Retro-Diels-Alder-reaction takes place.

Über das optische Drehungsvermögen des Crocins in echter und in kolloider Lösung

ZusammenfassungDas optische Drehungsvermögen des Crocins ist in kolloider Lösung erstaunlich hoch, in echter Lösung äußerst gering.