Properties of porcine platelet myosin. II. Shape change of the molecule

Porcine platelet myosin molecules were examined by electron microscopy for changes in their shape. At high ionic strength, the molecules were morphologically indistinguishable from skeletal muscle myosin, except for a slight difference in the bent regions of their tails. At physiological ionic strength, however, the following important difference was observed between the two myosins. Unlike skeletal muscle myosin, the filaments of nonphosphorylated platelet myosin could be disassembled by stoichiometric ATP into a monomeric form with sharply bent or folded tail, and reassembled after ATP hydrolysis. Similar disassembly changes could be induced by various nucleotide triphosphates (CTP, GTP, ITP, and UTP) and to a lesser extent by ADP, AMP, and AMPPNP. These results suggest that ATP binds to the hydrolytic sites in platelet myosin molecule and induces the molecular shape change.     

Fine structural and immunohistochemical studies of goat adenohypophysial cells

Summary The fine structure of each type of anterior pituitary cell in the male goat was studied through the application of a superimposition technique in which adjacent thick sections were used to identify individual cells beforehand by light-microscopic immunohistochemistry. A cone of the pars intermedia protrudes into the pars anterior, being surrounded by the narrow pituitary cleft; the immunohistochemical appearances of the cells forming the cone resemble those of the pars anterior. Several follicles appear in the pars anterior. Ultrastructurally GH cells resemble prolactin cells. The secretory granules of both types are spherical; the diameter of the former is about 340 nm, whereas that of the latter is about 440 nm. ACTH cells are polygonal in shape with secretory granules, about 180 nm in diameter, scattered throughout the cytoplasm. TSH cells, which are spherical in shape, contain the smallest secretory granules, 150 nm in diameter. The highly electron-dense LH cells contain numerous secretory granules about 210 nm in diameter. Their nuclei are irregular with incisures. Thus, the anterior pituitary cells of the goat are ultrastructurally characteristic and species-specific.     

Studies on cation-induced membrane vesicle aggregation of porcine intestinal brush borders

Protein alterations during the development of the mouse brain were studied by two-dimensional gel electrophoresis. A protein spot with a molecular weight (MW) of 68,000 and pI value of 5.6 was found in the brain of the 11th day of gestation. Between the 12th and the 14th day of gestation, spots with the same MW and lower pI values appeared progressively. Neuraminidase digestion converted the pI of these acidic spots to 5.6. Thus, increased sialylation appeared to occur during this period. This class of molecules became hardly detectable on the 15th day, and disappeared completely after the 16th day. Analogous spots were present in the heart, liver, and stomach of the embryos, although the increased sialylation was not observed in the liver. No adult organs so far examined showed these spots. On the other hand, two polypeptides (MW 55,000, pI 4.7, and 53,000, pI 4.6) appeared in the brain on the 13th day of gestation and persisted throughout the fetal period. After birth, they became hardly detectable. Furthermore, a spot (MW 48,000, pI 4.8) became newly detectable in the brain 4-5 weeks after the birth.     

Do protozoa conceal a high potency of nucleoside triphosphate hydrolysis present in Toxoplasma gondii?

ATP hydrolytic activity in whole cell homogenates of some protozoa was assayed in the presence or absence of dithiothreitol. The activities in all protozoan cell homogenates, except Toxoplasma gondii, ranged from 0.6 to 32 mumol/mg protein/hr, irrespective of the presence or absence of dithiothreitol. A remarkably higher activity, 11,690 mumol/mg protein/hr, was observed for T. gondii in the presence of dithiothreitol. These results indicate that the higher ATP hydrolytic potency observed for T. gondii is not universal to protozoa, rather it is unique to T. gondii.     

Molecular and enzymatic properties of 1,2-α-d-mannosidase fromAspergillus saitoi

The molecular properties, such as molecular weight, N-and C-terminal amino acids, amino acid composition, and circular dichroism, of 1,2--mannosidase isolated from the culture filtrate ofAspergillus saitoi were determined.The enzyme had aK _m of 0.67 mM andk _cat of 1.27/s with mannobiose at pH 50.0 and 30°C. The anomeric configuration of the reaction products of the enzyme was examined by studying the -anomer. A single Manl2Man linkage in intact Taka-amylase A fromAspergillus oryzae was hydrolyzed, producing free mannose.     

Wound healing in the cornea of the chick embryo

Spatio-temporal changes in the shapes of the epithelial cells in culture were followed with the aid of scanning electron microscopy. On a substratum that enables the epithelium to spread extensively, the first remarkable change in shapes of the cells occurred at the margin of epithelium at 12 h of culture. The marginal cells formed leading edges with filo- or lamellipodia, flattened, and lost microvilli on surface. In accordance with those changes, the borderlines among cells became almost indiscrenible. Flattening of the cells was the essential characteristic associated with active epithelial spreading throughout the culture period. Elongation of cells of intermediate zone at right angles to the direction of the locomotion of the marginal cells at 24 h of culture was the second significant change. As the third, the change from the ordinary pentagonal or hexagonal to extraordinary tetragonal or other polygonal shapes, with or without irregular margins, began in cells of the intermediate area at 24 h and propagated to those in inner area. The active deformation of the inner cells with no space in which to move was considered to play some role in the extensive epithelial spreading.     

Studies on extracellular ribonucleases of Ustilago sphaerogena. Purification and properties

1. Four ribonucleases were isolated from culture media of Ustilago sphaerogena. They were designated ribonucleases U(1), U(2), U(3) and U(4). 2. They were purified about 1600-, 3700-, 1100- and 16-fold respectively. 3. It was shown by gel filtration that ribonucleases U(1), U(2) and U(3) have molecular weights about 10000 like ribonuclease T(1), and that ribonuclease U(4) is much larger. 4. Ribonucleases U(1), U(2) and U(3) are thermostable, but ribonuclease U(4) is not. 5. The pH optimum of ribonucleases U(1) and U(4) is pH8.0-8.5, and that of ribonucleases U(2) and U(3) is pH4.5.