Multiple-bond kinetics from single-molecule pulling experiments: evidence for multiple NCAM bonds.

The kinetic parameters of single bonds between neural cell adhesion molecules were determined from atomic force microscope measurements of the forced dissociation of the homophilic protein-protein bonds. The analytical approach described provides a systematic procedure for obtaining rupture kinetics for single protein bonds from bond breakage frequency distributions obtained from single-molecule pulling experiments. For these studies, we used the neural cell adhesion molecule (NCAM), which was recently shown to form two independent protein bonds. The analysis of the bond rupture data at different loading rates, using the single-bond full microscopic model, indicates that the breakage frequency distribution is most sensitive to the distance to the transition state and least sensitive to the molecular spring constant. The analysis of bond failure data, however, motivates the use of a double-bond microscopic model that requires an additional kinetic parameter. This double-bond microscopic model assumes two independent NCAM-NCAM bonds, and more accurately describes the breakage frequency distribution, particularly at high loading rates. This finding agrees with recent surface-force measurements, which showed that NCAM forms two spatially distinct bonds between opposed proteins.

On the "Identification and control of dynamical systems using neural networks".

Referring to the above said paper by Narendra-Parthasarathy (ibid., vol.1, p4-27 (1990)), it is noted that the given Example 2 (p.15) has a third equilibrium state corresponding to the point (0.5, 0.5).

Changes in the pattern of microsomal fatty acids in rat liver after thermal injury and therapeutic intervention.

Despite substantial progress in handling the acute phase after thermal injury, severely burned patients still succumb to systemic sepsis as a consequence of a compromised defence system. It is likely that autotoxic mechanisms play an important role in the aetiology of the impaired host defence. One of the primary target systems of autotoxic cell damage is the liver. In the present work oxidative alterations in the microsomal compartment of liver cells have been investigated. It was found that thermal burns are associated with extensive oxidation of polyunsaturated fatty acids which can be antagonized by antioxidants such as silibinin.

Damage in vitro to various organs and tissues by rubescenslysin from the edible mushroom Amanita rubescens.

Rubescenslysin, a haemolytic protein from Amanita rubescens, disrupted the cytoplasmic membrane of human leucocytes which were more sensitive than erythrocytes. In the isolated hearts of rats and guinea pigs it caused systolic contracture, which was preceded by potassium outflow and sometimes by a transient positive inotropic effect. On the electrically stimulated guinea-pig left atrium it showed at first a positive, followed by a negative inotropic effect; on the spontaneously beating right atrium it produced transient positive followed by negative inotropic and chronotropic effects. Atria were less sensitive than intact hearts. In the isolated rat phrenic nerve-diaphragm preparation it produced a contracture, which was associated with reduction of indirect and direct contractility. In the isolated guinea-pig ileum it produced a slow contraction followed by tachyphylaxis. As excitability declined due to rubescenslysin, so did excitability by acetylcholine and potassium. Atropine and pheniramine had only feeble antagonistic effects, but papaverine was more powerful. In isolated rat hepatocytes, rubescenslysin caused a rapid outflow of potassium and coarse cell protrusions while later the cells became stainable with trypan blue. In the isolated perfused rat liver it produced a rapid outflow of potassium and of cytoplasmic and mitochondrial enzymes, and a somewhat slower outflow of lysosomal beta-glucuronidase, accompanied by a rise in the lactate/pyruvate ratio and a decrease in bile production. In the isolated perfused rat kidney it caused an outflow of cytoplasmic and mitochondrial enzymes, together with massive proteinuria and serious restriction of sodium and potassium reabsorption and of urine output. In all the tissues investigated the effects of rubescenslysin began within a few min, were dose-dependent and practically irreversible. There were only minor differences in sensitivity between various organs and species. The observations indicate that the toxin is relatively nonspecific in its attack on components of cell membranes.

On the nephrotoxicity of alpha-amanitin and the antagonistic effects of silymarin in rats.

In human beings, poisoning by the deathcup mushroom causes renal lesions in addition to extremely severe liver damage. It is known from animal experiments that silymarin, a polyhydroxyphenylchromanone, is capable of counteracting this alpha-amanitin-induced liver damage. The purpose of the present work was to ascertain whether renal damage could be induced in rats by giving alpha-amanitin, and whether silymarin would have any effect on such renal damage. The fact that alpha-amanitin produces pathological changes in the kidneys and that these lesions can be almost completely prevented by pretreating rats with silymarin has now been amply demonstrated by biochemical and histological techniques alike.