Endogenous formation of dimethylamine.

Exposure of rats to heat (39 +/- 1 degree C) decreased H2O2 generation in mitochondria of the liver, but not of the kidney or the heart. The effect was obtained with three substrates, succinate, glycerol 1-phosphate and choline, with a decrease to 50% in the first 2-3 days of exposure, and a further decrease on longer exposure. The dehydrogenase activity with only glycerol 1-phosphate decreased, which is indicative of the hypothyroid condition, whereas choline dehydrogenase activity remained unchanged and that of succinate dehydrogenase decreased on long exposure. The serum concentration of thyroxine decreased in heat-exposed rats. Thyroxine treatment of rats increased H2O2 generation. Hypothyroid conditions obtained by treatment with propylthiouracil or thyroidectomy caused a decrease in H2O2 generation and changes in dehydrogenase activities similar to those with heat exposure. Treatment of heat-exposed or thyroidectomized rats with thyroxine stimulated H2O2 generation by a mechanism apparently involving fresh protein synthesis. The results indicate that H2O2 generation in mitochondria of heat-exposed animals is determined by thyroid status.     

Mechanics of Rouleau formation.

The formation of rouleau of red blood cells is considered from the standpoint of adhesion theory. With the use of the elastic properties of the red blood cell membrane obtained from previous work, the strain energy of the red blood cell in rouleau formation has been computed. The surface energy of adhesion for the bonding of two red blood cells is then computed from the variation of this strain energy. Computed cell shapes agree well with experiments.     

Prostaglandin formation in bacteria.

We report here that intact Gram positive and Gram negative bacteria, in the presence of exogenous arachidonic acid, produce and release PGE2 and PGF2 alpha into the medium as measured by radioimmunoassay. The seven bacterial strains so far studied release 6.5-50.9 ng PGE2 and less than 0.02-0.51 ng PGF2 alpha per mg bacterial protein during a 1 hour incubation, quantities of the same order of magnitude as those observed in mammalian systems. PGE2 and PGF2 alpha formation in bacteria are inhibited by indomethacin.     

Follicle formation in the embryonic chick thyroid. III. Initiation of follicle formation

It has been proposed that the follicular spaces in the thyroid form by either the coalescence of intracellular droplets or by separation of cell apices by secretion into the extracellular space. On the basis of examination of thyroid primordia in early chick embryos this study provides evidence that in the chick, at least, follicle formation conforms to the second model. The first indications of change in the chick thyroid is the appearance of interdigitations of the cell apices. These interdigitations form microvilli as the two surfaces become separated and the follicular space is established. Vesicles with two types of contents can be identified in proximity with the cell surface during follicle formation, but it is not clear if either the dense particulate or the more electron-lucid materials that they contain actually enter the follicular space. Neither removal of the pituitary gland by decapitation nor inhibition of collagen synthesis and a concomitant failure of the invasion of capsular mesenchyme prevents the initiation of normal follicle formation.     

RNA-catalyzed carbon-carbon bond formation.

RNA molecules with catalytic properties have been isolated by in vitro selection from combinatorial libraries. A broad range of chemical reactions can be catalyzed, and nucleic acids can accelerate bond formation between small organic substrates. The catalytic performance of nucleic acids can be enhanced by incorporation of additional functional groups. This minireview focuses on carbon-carbon bond formation accelerated by in vitro selected ribozymes.