Ionic strength dependent enzyme activities of elastase

Summary Peptidase and esterase activities of elastase were each altered separately by the ionic strength of the buffer used. The esterase activity is exerted in a lower ionic strength medium where the peptidase activity is not detected.     

Binding of iproniazid to the polymeric forms of iodide peroxidase

Summary ¹⁴C labelled iproniazid binds to iodide peroxidase more effectively in low ionic strength buffer than in high ionic strength buffer, suggesting preferential binding to the monomeric form of iodide peroxidase. During column chromatography, under conditions that separate iodide peroxidase into multiple forms, iproniazid is bound selectively to the monomeric form. Thus, this antithyroid agent appears to bind preferentially to the monomeric enzyme form, or possibly to cause dissociation of the polymeric to the monomeric form.Supported in part by United States Public Health Service Grants AM-13,377 and AM-13,643.     

Ionic control of biochemical reactions]

It is shown that pH and ionic strength are tightly interdependent in cytochrome oxidase activity at the level of inner membranes of the mitochondrion, as a direct consequence of the polyanionic environment of this enzyme. Application of polyelectrolyte theory explains a number of biochemical reactions controlled by ionic strength fluctuations.     

Parameters influencing inactivation-dissociation/reactivation-association phenomena induced by variations of ionic strength of L (+)lactate: cytochrome c oxidoreductase (cytochrome b2) extract of the yeast Hansenula anomala

H-flavocytochrome b2, a tetramer enzyme, is inactivated, at low ionic strength and can be reactivated, increasing the ionic strength of the medium. The inactivation-reactivation process was structurally manifested by a dissociation-association phenomenon between subunits. It was clearly shown that the inactivation-dissociation process appeared independent of enzyme concentration whereas the reactivation-association phenomenon was enzyme concentration dependent. However, proteins protect H-flavocytochrome b2 from inactivation-dissociation, only when electrostatic interactions are possible between the two proteins: Horse heart cytochrome c was a good protector whereas serum albumin had no protector effect.     

Effect of the ionic strength on the kinetic properties of the mitochondrial L-malate dehydrogenase

Increase of the ionic strength inhibits the catalytic activity of the mitochondrial MDH, reduces substrate inhibition and decreases the affinity of the substrates for the enzyme.     

Effect of the ionic strength on the kinetic properties of the mitochondrial L-malate dehydrogenase

Summary Increase of the ionic strength inhibits the catalytic activity of the mitochondrial MDH, reduces substrate inhibition and decreases the affinity of substrates for the enzyme.This work was supported by a grant from the Conselho Nacional de Desenvolvimento Tecnológico (CNPq), Brazil.     

Purification of diphtheria toxin by chromatography on Cibacron Blue-Sepharose

Diphtheria toxin binds to Cibacron Blue-Agarose and may be eluted by increasing the ionic strength of the elution buffer. Experiments using difference spectroscopy showed that the interaction between toxin and dye is ionic rather than hydrophobic, and therefore it is of a different nature with respect to that usually found in nucleotide-requiring enzymes.     

Purification of the vascular plasminogen activator]

We have isolated a purified preparation of the vascular plasminogen activator. Plasma obtained from post occlusion venous blood has been chromatographed with low and high ionic strength buffers. The purified protein has a relative molecular weight of 71,000.     

Cooperative non-specific binding of the cyclic adenosine 3'--5'-monophosphate receptor protein (CRP) from Escherichia coli to double-stranded thymus and lambda pgal DNA]

Either free or combined with cAMP, CRP binds cooperatively to double-stranded thymus and lambda pgal DNA. The affinity of CRP for both DNAs in these non-specific interactions is increased by cAMP without noticeable change in the degree of cooperativity. Values of the intrinsic association constant, cooperativity parameter, and site size of DNA were determined from ultracentrifugal investigations under near-physiological ionic conditions.     

Protein methylase from calf liver nuclei: enzyme characterization and stimulation by serum albumins.

A protein methylase from calf-lifer nuclei was partially purified by sonication of the nuclear pellet at high ionic strength, chromatin removal and ammonium sulphate fractionation of the solubilized activity.     

Solubilization of unconjugated bilirubin by bile salts.

Freshly precipitated unconjugated bilirubin (UCB) is solubilized rapidly and to a large extent by the sodium salts of di- and trihydroxy bile acids. The solubilization effect depending on bile salt concentration, pH and ionic strength is based on micellar mechanisms.     

Solubilization of unconjugated bilirubin by bile salts

Summary Freshly precipitated uncojugated bilirubin (UCB) is solubilized rapidly and to a large extent by the sodium salts of di- and trihydroxy bile acids. The solubilization effect depending on bile salt concentration, pH and ionic strength is based on micellar mechanisms.     

Die Abhängigkeit der Magnesium-‘aktivierten Inosin’ Triphosphatase-Aktivität des Aktomyosins von der Ionenstärke

Summary The ionic strength dependence of the magnesium-activated actomyosin ITPase activity (of heart and skeletal muscle) is distinctly different from that of the magnesium-activated ATPase activity. The former is inhibited by lowering the ionic strength below 0.1 , an effect which can be attributed to an ionic strength dependent inhibitory action of tropomyosin B.

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Herrn Prof. Dr.J. C. Rüegg danke ich für viele wertvolle Diskussionen und das kritische Durchlesen des Manuskriptes. Ebenso bin ich Herrn Dr.M. C. Schaub für viele hilfreiche Diskussionen und die Mitteilung unveröffentlichter Resultate zu Dank verpflichtet. FräuleinL. Mintert und meine FrauGeraldine möchte ich auf Grund der ausgezeichneten technischen Assitenz lobend hervorheben.     

Are intermediate filaments of vertebrate smooth muscle cells and tonofilaments of epithelial cells identical cell structures?

Summary In epithelial and smooth muscle cells of the urinary bladder of the frog, a class of filaments exists which is partly disintegrated by glycerol treatment and very resistant to potassium solutions of high ionic strength.We are indebted to Miss M. Schlatter for her technical assistance. This work was supported by the Deutsche Forschungsgemeinschaft (He 686/2).     

Electrophorèse de protéines musculaires de Lapin

Summary Saline extracts from rabbit's skeletal muscles obtained and dialyzed at the ionic strength 0.15 contain at least 11 electrophoretically distinct components. Five of these components (n, m, t, l, s) have properties which are comparable with some characteristics of the myogens ofWeber, another component (h) is probably myoalbumin. Muscular proteins which are more soluble at higher ionic strength are not homogenous: there must be not one but two or more electrophoretically different myosins. Much work is needed to establish accurate relations between electrophoretic and classical muscular proteins.     

Alkyltransferase-like proteins: molecular switches between DNA repair pathways

Alkyltransferase-like proteins (ATLs) play a role in the protection of cells from the biological effects of DNA alkylation damage. Although ATLs share functional motifs with the DNA repair protein and cancer chemotherapy target O ⁶-alkylguanine-DNA alkyltransferase, they lack the reactive cysteine residue required for alkyltransferase activity, so its mechanism for cell protection was previously unknown. Here we review recent advances in unraveling the enigmatic cellular protection provided by ATLs against the deleterious effects of DNA alkylation damage. We discuss exciting new evidence that ATLs aid in the repair of DNA O ⁶-alkylguanine lesions through a novel repair cross-talk between DNA-alkylation base damage responses and the DNA nucleotide excision repair pathway.     

If the cap fits,wear it: an overview of telomeric structures over evolution

Genome organization into linear chromosomes likely represents an important evolutionary innovation that has permitted the development of the sexual life cycle; this process has consequently advanced nuclear expansion and increased complexity of eukaryotic genomes. Chromosome linearity, however, poses a major challenge to the internal cellular machinery. The need to efficiently recognize and repair DNA double-strand breaks that occur as a consequence of DNA damage presents a constant threat to native chromosome ends known as telomeres. In this review, we present a comparative survey of various solutions to the end protection problem, maintaining an emphasis on DNA structure. This begins with telomeric structures derived from a subset of prokaryotes, mitochondria, and viruses, and will progress into the typical telomere structure exhibited by higher organisms containing TTAGG-like tandem sequences. We next examine non-canonical telomeres from Drosophila melanogaster, which comprise arrays of retrotransposons. Finally, we discuss telomeric structures in evolution and possible switches between canonical and non-canonical solutions to chromosome end protection.     

Ambiquitous behavior of rabbit liver lactate dehydrogenase

Rabbit liver mitochondrial fraction shows lactate dehydrogenase activity. The enzyme can be released from particles by increasing the pH and the ionic strength of the medium. There is a narrow range of pH (6.8-7.4) and ionic strength (20-50 mM NaCl) in which the solubilization sharply increases. It has been shown that divalent anions (SO4(2-) and cations (Mg2+, Ca2+) are highly effective specific solubilizing agents. NADH (1.5 mM) and ATP (1.0 mM) were effective in solubilizing 50% of the enzyme bound, whereas the same concentrations of the analogs NAD+ and ADP had little effect. Cytosolic lactate dehydrogenase bound to the mitochondrial fraction and a saturation of particles by enzyme was observed in all experiments performed. The in vitro binding requires a short period of incubation between the enzyme and particles and the binding is independent of the temperature in the 0-37 degrees C range. Binding was prevented by 0.15 M NaCl. The bound enzyme is approximately 20% less active than the soluble one. The results described give support to the proposal that rabbit liver lactate dehydrogenase has an ambiquitous behavior, like other glycolytic enzymes, which have not a fixed intracellular localization.     

Influence of mono-and multivalent cations on the electrokinetic properties of normal human lymphoid and Burkitt lymphoma cells

Summary Various mono- and multivalent cations, at constant ionic strength, affected the surface electrokinetic properties of normal human lymphoid and Burkitt lymphoma cells in a manner which reflected more the physicochemical properties and binding affinities of the cation than its valence. The effect was expressed in the changes of the magnitude of the net surface charge and in the shift of the isoelectric point of the surface. These changes were greater atthe surface of Burkitt's lymphoma cells than at the surface of their normal cell-line counterparts.     

Heterogeneity of HeLa cell DNA as evidenced by CsCl density gradient centrifugation

Summary HeLa cell DNA was analyzed through CsCl density gradient centrifugation and thermal denaturation. Neutral centrifugation without ionic treatment allowed the resolution of a main peak with density 1.699 g/ml and of 3 satellites DNAs with densities 1.683, 1.710 and 1.720. First derivatives of melting curves showed the presence of 4 DNA families, whose G+C content calculated from T_m values corresponded almost exactly to the G+C content expected from the previously densities. The extraction method seems particularly suitable for quantitative separation of DNA classes.