Elektrostatische Wechselwirkung zwischen gegensinnig geladenen Ionenaustauscher-Teilchen

Gegensinnig geladene Ionenaustauscher können sich elektrostatisch anziehen, was zu Verklumpung und stark vergrößertem Volumen des Harzgemisches führt. Es wird beschrieben, unter welchen Bedingungen diese Anziehung stattfindet. Um sie zu unterdrücken, sind geringe Zusätze feinst gemahlener Ionenaustauscher besonders wirksam

Zur struktur von mit divinylbenzol vernetzten polystyrol-lonenaustauschern

Es wird ein räumliches Molekülmodell vorgeschlagen, aus welchem der mittlere Durchmesser der die Diffusion von Ionen begrenzenden Strukturen berechnet werden kann. Elektronenoptische Aufnahmen an Dünnschnitten von lonenaustauschern werden gezeigt, welche die regelmäßige Netzstruktur klar erkennen und ausmessen lassen. Das Modell liefert eine größenordnungsmäßige Übereinstimmung sowohl mit den bei höheren Vernetzungsgraden aus Diffusionsversuchen bekannten begrenzenden Durchmessern als auch mit den bei niedrigen Vernetzungsgraden aufgenommenen Aufnahmen

Über Actin-Nucleotide und die Funktion und Bindung der Nucleotidphosphate im G- und F-Actin

1. If pure F-actin-ADP * which is free of enzymes is depolymerized G-actin-ATP * arises in the presence of 10-4 M ATP, G-actin-ITP * in the presence of 10-4 M ITP, and G-actin-ADP in the presence of 10-4 M ADP. If the depolymerization takes place in the absence of free nucleotide phosphate G-actin-ADP also arises. If G-actin-ADP is added to a solution containing 10-4 M ITP or ATP the bound ADP is exchanged with ATP respectively with ITP (Section II). 2. G-actin-ATP and G-actin-ITP polymerize to F-actin-ADP and to F-actin-IDP respectively by splitting off the γ-phosphate of the ATP or ITP. G-actin-ADP polymerizes to F-actin-ADP without splitting off phosphate. The polymerization of G-actin-ADP is as complete as the polymerization of G-actin-ATP; but the process is perceptibly shower (Section II). 3. G-actin that is not bound to a nucleotide phosphate does not polymerize (Section II). 4. G-actin-ADP in the absence of free ADP spontaneously disintegrates in a half-life of 70 minutes to yield G-actin and ADP. If the dissociating ADP is continuously removed by being bound to Dowex 1 × 10 the half life drops to 7 to 8 minutes. In the presence of Dowex G-actin-ATP disintegrates in a half life of 240 minutes (Section III). 5. The disintegration of G-actin-ADP takes place in two stages. A reversible dissociation into ADP and G-actin I is followed by an irreversible denaturation of G-actin I to G-actin II in a half life ~ 12 minutes. Contrary to actin I G-actin II even on the addition of ATP no longer polymerizes. The difference in the half life of pure G-actin-ADP on the hand and of G-actin-ADP+ADP as well as G-actin-ATP on the other must be attributed to the relatively high equilibrium concentration of G-actin I in the first case and of the relatively slight equilibrium concentration of G-actin I in the second case (Section IV). 6. If the alkaline earth of G-actin is blocked by 10-3 M EDTA G-actin-ATP disintegrates in a half life ∼ 3 minutes and G-actin-ADP in a half life ∼ 0,3 minutes. On the other hand, the stability of F-actin-ADP is not noticeably affected (Section V). 7. Through a two hour rapid dialysis in the presence of 10-4 M ATP the KCl-content of an F-actin-ADP solution drops to 5 × 10-4 M KCl. In spite of this the depolymerization and exchange of ADP with ATP is finished not before 40 hours if the solution remains at rest. If, however, the actin solution containing 5 × 10-4 M KCl is treated with the Teflon homogenizer for about 30 sec. depolymerization and ADP-ATP-exchange occur immediately. On the contrary, F-actin-ADP in 10–1 M KCl solution is not affected at all by a treatment with the Teflon-homogenizer. Apparently the decrease of the KClconcentration from 10-1 M to 5 × 10-4 M considerably diminishes the strength of the bond between the actin monomers without immediately destroying the F-actin arrangement. The immediate ADP-ATP-exchange after the mechanical destruction of the F-actin arrangement proves that this exchange in F-actin does not take place only because of steric hindrance. ADP is present in F-actin apparently between the individual monomers so that EDTA, ATP and enzymes affecting ATP cannot approach ADP. Consequently it is not necessary to assume that the extraordinary stability of F-actin-ADP is due to a special kind of bond between actin monomers and nucleotide phosphate (Section V). 8. In the appendix it is shown that G-actin-ADP does not polymerize 15′ after preparation if the aceton dried muscle powder is prepared at pH 8 to 9 instead of pH ∼ 7

Die erschöpfende Reinigung von Aktin-Präparaten Zahl und Art der phosphathaltigen prosthetischen Gruppen von G- und F-Aktin

Exhaustive purification of actin preparations. Number and kind of phosphate containing prosthetic groups of G- and F-actin 1. 1. Previous investigations on the nucleoside phosphate content of G- and F-actin have all been carried out with unpurified or little purified protein preparations. It has never been tested whether the purification was complete or whether the purification itself inactivated the preparation. 2. 2. In F-actin solutions prepared according to Straub the content of adenine decreases by repeated ultracentrifugal sedimentation or Mg-precipitation according to Bárány to a constant level which is identical with both methods (16 μmoles/g protein). The adenine and phosphate content of the actin remains constant after the second purification procedure. Both procedures remove protein impurities present in the crude extract. 3. 3. The protein impurities are, however, not removed by repeated isoelectric precipitation of the crude unpolymerized Straub-extract. This procedure removes only contaminating phosphate and nucleoside phosphate of the crude extract. The actin polymerizes spontaneously during isoelectric precipitation. 4. 4. Ultracentrifugal sedimentation of F-actin, precipitation by MgCl2 or isolectric precipitation in presence of ATP do not inactivate the actin. The viscosity of F-actin, the ability for activating the ATP-ase of added L-myosin and the ATP-sensitivity of the resulting actomyosin remain constant even after repeating the purification procedure five times. 5. 5. Repeated isoelectric precipitation of actin in absence of ATP leads to an increasing loss of adenine phosphate and also to a stepwise decrease of Zν and ATP-sensitivity. 6. 6. In the nucleoside phosphate of purified F-actin the proportion of adenine to phosphate is 1:2 as in ADP. Paperchromatographic methods reveal in addition traces of AMP and ATP. 7. 7. G-actin and the contaminating proteins in the crude extracts contain also 16 μmoles adenine/g protein. 8. 8. From the content of adenosine phosphates bound to G- or F-actin (16 μmoles/g protein) the minimal molecular weight of the actin monomer is calculated as 62.000. 9. 9. The proportion adenine: phosphate and paperchromatographic methods show, that in the crude unpolymerized extract the protein-bound nucleoside-phosphate consists of 70–75% ATP and 25–30% ADP. Only 70–75% of the protein in the crude extract are able to polymerize. 10. 10. However, G-actin obtained from purified F-actin containing also 70–75% of its nucleoside phosphates as ATP does polymerize entirely. Thus whether or not ADP-G-actin polymerizes seems to depend on the history of the protein preparation. 11. 11. G-actin, whose ability for polymerization has been destroyed by X-rays, nevertheless activates the L-myosin-ATP-ase to a normal extent. The same holds for actin partly denatured by isoelectric precipitation in the absence of ATP. Thus, the ability of actin for polymerisation and its ability to activate the L-myosin-ATP-ase are independent properties. 12. 12. In phosphate or ATP containing solutions, purified F-actin ATP and inorganic phosphate reversibly (in addition to the tightly bound ADP). Howeever, actin is not phosphorylated in presence of ATP