Inversion of a behavioral response in bacterial chemotaxis: explanation at the molecular level

Certain cheU mutants of Salmonella show inverted chemotactic behavior, being repelled by attractants and attracted by repellents. Such a dramatic change in behavioral pattern would seem at first glance to require drastic and complex alterations in the sensory processing system. In fact, the behavior can be explained by a simple shift in the level of a response regulator and the subtle effects of this shift on flagellar function. Flagella can exist in either a left-handed or a right-handed structure depending on applied torsion. Wild-type cells swim smoothly by counterclockwise rotation of a left-handed helical bundle and tumble when the motors briefly reverse to clockwise rotation (normal random motility). The cheU mutation causes a shift in response regulator level relative to the critical threshold value, resulting in extended clockwise operation so that the flagella are fully converted to the right-handed helical form. These cells therefore swim smoothly by clockwise rotation of a right-handed bundle and tumble when the motor briefly reverses to counterclockwise rotation (inverse random motility). Thus, tumbling is associated with brief reversals and not with a particular sense of rotation. A wild-type cell, with its steady-state response regulator level placing it initially in normal random motility, will swim smoothly on addition of attractant, whereas a cheU mutant with inverse random motility will tumble given the same stimulus. The phenomenon illustrates the profound behavioral consequences that can result from a single mutation in a key gene.

Alteration of myoblast phenotype by dimethyl sulfoxide

Application of dimethyl sulfoxide to proliferating L8 myoblasts (an established cell line of rat skeletal muscle) for 72 hr completely prevented fusion and induction of creatine phosphokinase (EC 2.7.3.2) activity (an indicator of muscle differentiation). The growth pattern changed from the usual sheets of randomly oriented cells to flattened, whorled monolayers of elongated fibroblast-like cells. By electron microscopy, rough endoplasmic reticulum increased and extracellular material appeared that had the morphologic and staining characteristics of collagen. After 120 hr in dimethyl sulfoxide-containing medium, the cells secreted about 6 times more collagen than untreated controls. Dimethyl sulfoxide was ineffective when applied to L8 cells just prior to fusion, and effects of dimethyl sulfoxide were not readily reversible unless treated cells were subcultured at low density.

Adsorption of oxamyl on montmorillonites

The adsorption of oxamyl under variable conditions of time, pH and exchangeable cations on montmorillonites has been examined. Kinetic studies showed the reaction to be first order, which indicates diffusion-controlled adsorption. All the evidence obtained by studies of the effect of pH, adsorption isotherms, considerations of the chemical structure of the molecule, and X-ray diffraction and infrared spectroscopy points to a reaction mechanism for oxamyl association with acid- and base-saturated montmorillonites which involves either protonation or coordination of the exchangeable clay cations to the carbonyl of the amide group.

Estradiol binding in ovariectomy-responsive and -nonresponsive rat mammary carcinoma

MTW9, a transplantable mammary tumor in Wistar-Furth rats, is dependent upon high levels of serum prolactin for growth. The mammary tumor can be maintained by coimplantation with a pituitary mammosomatotropic tumor (MTW9-MtT) or by chronic perphenazine administration (MTW9-P). MTW9-MtT does not regress after ovariectomy (OVEX) alone, while, MTW9-P regresses rapidly whether or not rats are maintained on perphenazine. Cytosol estradiol binding was determined in MTW9-MtT, 47.6 +/- 3.6 (N = 9), Kd 9.9 +/- 2.0 X 10(-11) M; MTW9-P, 195.5 +/- 9.1 (n = 16), Kd 27.6 +/- 4.7 X 10(-11) M; MTW9-P after perphenazine was withdrawn, 86.0 +/- 6.0 (n = 6), Kd 9.9 +/- 1.5 X 10(-11) M. Eight S and 4 S peaks were found in cytosols from both tumors by sucrose gradient centrifugation; the peaks differ qualitatively and quantitatively. The possibility that differences in binding levels result from sites filled with endogenous estradiol was critically examined and rejected. Withdrawal of perphenazine results in reduction of estradiol binding but retention of response to OVEX. Hence, response of MTW9-P to OVEX cannot be explained by the 3- to 4-fold increase in estradiol binding over MTW9-MtT. The relationship between estradiol binding and response to OVEX is under study using both mammary tumor models.

The scanning electron microscopy of the lysis of fibrin by endothelium

The lysis of a fibrin clot by sheets of endothelium one cell thick was examined by scanning electron microscopy. The unlysed fibrin film appeared as a densely matted surface, without interstices. Commencing lysis appeared as parallel ovals in which the dense matting was altered to show many strands of fibrin criss-crossing the lytic "window" with many interstices. The wall of the lytic crater surrounding the sheets of endothelium revealed a network of fibrin strands. There was condensation of the fibrin at the edge of the hole at the external surface. The floor of the crater contained sheets of endothelium which were recognized by the shape and size of the nuclei. Flocculent masses of precipitate were present on the endothelial cells in the floor of the crater and occasionally within the lysed ovals at the edge. These may be fibrin degradation products.

Tetracycline and acne vulgaris: a clinical and laboratory investigation

A satisfactory clinical response to long-term oral tetracycline treatment was associated with a mean serum tetracycline of 1.98 mug/ml. The surface lipid showed an increased triglyceride, decreased free fatty acids, and decreased cholesterol, and the amount of keratin within the pilosebaceous duct was reduced. At this dose level there was no quantitative decrease in the bacterial flora though there was a decrease in the fatty acids. We believe that the latter was due to a direct inhibition by tetracycline on extracellular lipases.