The Contractile and Control Sites of Natural Actomyosin

The various contractile and control sites of natural actomyosin gel were studied by comparing the kinetics of ATP hydrolysis with those of gel contraction, measured as an increase in turbidity. Contraction of actomyosin gel seems to require the cooperative reaction of ATP (with Mg) at two different sites. One of these sites catalyzes the hydrolysis of ATP and most probably contributes the driving force for contraction; the binding of ATP to the other site appears to break certain links that retard movement of the gel components. At limiting concentrations of ATP, the rate of contraction seems to depend on the rate of breaking these links as well as on the rate of ATP hydrolysis. But when both sites are saturated, the rate of contraction appears to be limited only by the rate of ATP hydrolysis. In addition to these two contractile sites, there are also two different control sites. At one, the relaxing site, the binding of ATP with Mg inhibits ATP hydrolysis and gel contraction. At the other, the binding of calcium activates contraction by overcoming the inhibitory action of Mg and ATP at the relaxing site. This control system—inhibition by substrate and disinhibition by calcium—can be selectively inactivated by heat and reactivated by dithiothreitol, a disulfide-reducing agent. These observations on the isolated contractile system are discussed in relation to the contraction and relaxation of muscle.     

Protein synthesis by microsomal particles from regenerating rat liver

1. Washed microsome particles from regenerating liver were shown to incorporate [(14)C]leucine into protein more actively than similar preparations from normal liver. 2. The total incorporation in the preparations from regenerating liver increased linearly with the amount of protein incubated, whereas this was not so with preparations from normal liver. 3. The greater activity of regenerating-liver microsomes appeared to be associated with the bound polysomes. 4. The size distribution of polysomes obtained after removal of membrane with deoxycholate was the same in normal and regenerating liver. 5. In general the activity of polysome preparations from normal and regenerating liver was similar. 6. It is concluded that the greater activity of the particles in the microsome fraction from regenerating liver is to be attributed to the ribosomes bound to membrane and that their activity is controlled by factors present in the membrane.     

Effect of exogenous serum gonadotrophin (PMS) on aspects of reproductive development in female domesticated canaries

PMS was injected thrice weekly for four weeks into first winter and second winter canaries during the following periods: September-October, November-December, January-February and February-March. Measures were made of ovary and oviduct weight, brood-patch development (defeathering, vascularity and sensitivity changes), nest-building and egg-laying. PMS caused overy growth in all months: this was greatest in the second year birds in February. Both control and treated ovaries increased in size towards the breeding season. Oviduct growth depends mainly on the size of the treated ovary. Defeathering was produced by PMS in all months: its rate and extent increased towards the breeding season. Vascularity was also produced by PMS. It was least in November-December but after that the rate at which it appeared increased towards the breeding season. By contrast, the effect of PMS on brood-patch skin sensitivity was greater in the autumn group than subsequently. Nest-building occurred in September-October, but was then very slight until February-March, which is the beginning of the breeding season. Eggs were laid in most months; fewer injections were needed to produce egg-laying as the breeding season approached.     

OBSERVATIONS ON LEAF AND BUD FORMATION IN HYDROCHARIS MORSUS-RANAE

Regular sequences of leaf and bud formation occur in several members of the Hydrocharitaceae, including Hydrocharis, in which buds are normally formed in the axil of every second leaf of the phyllotactic spiral. Leaf inception begins by periclinal divisions of the inner cells of the 2-layered tunica. Bud formation, which occurs in the apical meristem itself, immediately following the inception of the subtending leaf primordium, begins by divisions in various planes in the corpus, the 2 tunica layers remaining continuous throughout. The young bud meristem soon gives rise to a lateral bud, before leaf formation begins upon it. Because of these and other features, this species is one of considerable morphogenetic interest. Morphogenesis of the whole plant, and in particular the factors controlling the regular sequence of leaf and bud formation, have been and are being investigated experimentally.     

An Electron Microscope Study of Intranuclear Inclusions in Mouse Liver and Hepatoma

An electron microscope study of intranuclear inclusions which occur in giant cells in a transplantable mouse hepatoma and in enlarged liver cells in mice fed a diet containing bentonite demonstrates that these inclusions are formed by invaginations of the nuclear envelope, and corroborates a previous histochemical study which revealed that the contents of the inclusions are of cytoplasmic origin. In the hepatoma cells the intranuclear inclusions are abundant, small, and situated close to the border of the nucleus, and there are wide openings from the cytoplasm into the invaginations whose contents include lipid droplets, ergastoplasm, and structurally normal mitochondria. In the enlarged liver cells the inclusions are fewer in number, generally much larger than those in the hepatoma, hence they extend deeper into the nucleus, and the interior is continuous with the cytoplasm through only a small opening. Some normal ergastoplasm is present within the inclusions but all other constituents are abnormal. Both normal and degenerating mitochondria occur in the cytoplasm but only degenerating ones are found within the inclusions. Both types of inclusions arise in greatly enlarged cells in which an attempt is made to maintain the normal nuclear surface/nuclear volume ratio by the development of the invaginations of the nuclear envelope.     

Effect of Phenolic Acids and Esters on Respiration and Reproduction of Bacteria in Urine

Vanillic, syringic, gallic, and protocatechuic acids, methyl-p-hydroxybenzoate, and propyl-p-hydroxybenzoate generally inhibited respiration in vitro of Escherichia coli, Proteus vulgaris, Pseudomonas aeruginosa, and Aerobacter aerogenes in human urine. In the absence of any other available carbon source, certain of the phenolic compounds were utilized. Reproduction was generally suppressed in urine buffered to pH 7, 5.6, 4.5, and 4.0. The phenolic compounds were used in the range of 0.11 to 0.99 μmole/ml.     

Characterization of Certain Gram-Negative Bacteria from Surface Waters

Cultures of gram-negative bacteria with oxidative glucose metabolism were isolated from surface waters by a highly selective technique, and were classified into 11 types. The predominant type, making up about 50% of the isolated cultures, was cytochrome oxidase-positive, produced fluorescent pigment, and failed to grow at 37 C. A similar type, which differed in being cytochrome oxidase-negative, constituted about 10% of the isolates. Both types of bacteria probably were composed of more than one species. A third type, composed of purple-pigmented pseudomonads, made up approximately 30% of the isolated cultures, and probably represented the predominant species. Other bacterial types isolated constituted less than 10% of the cultures examined.