Platelet-activating factor mobilizes intracellular calcium in vascular smooth muscle cells

The effect of platelet-activating factor (PAF) on polyphosphoinositide metabolism and 45Ca2+ efflux was examined in a vascular smooth muscle cell line (A7r5). PAF stimulated a rapid but transient production of inositol trisphosphate and inositol bisphosphate which, in the presence of lithium, resulted in an accumulation of inositol monophosphate. In addition, PAF induced a rapid efflux of 45Ca2+ from preloaded cells, an effect which was concentration-dependent. These data suggest that PAF mobilizes intracellular Ca2+ via the production of inositol trisphosphate.     

Specific effects of ATP on the kinetics of reconstituted bovine heart cytochrome-c oxidase

Bovine heart cytochrome-c oxidase was reconstituted in liposomes and the kinetics of cytochrome c oxidation were measured by the polarographic and photometric method under uncoupled conditions in the presence of various polyvalent anions. In order to distinguish between specific and unspecific ionic effects of ATP, the photolabelling reagent 8-azido-ATP was applied. Covalently bound ATP at the enzyme complex caused the same increase of Km for cytochrome c as free ATP, if measured by the photometric assay. The increase of Km by photolabelling with 8-azido-ATP was completely prevented by ATP, but not by ADP. The data indicate the occurrence of a specific binding site for ATP at the cytosolic side of cytochrome-c oxidase, which, after binding of ATP, changes the kinetics of cytochrome c oxidation.     

Prostaglandin-E2 9-ketoreductase from human uterine decidua vera

Prostaglandin-E2 9-ketoreductase, the enzyme which catalyzes the reaction from prostaglandin E2 (PGE2) to prostaglandin F2 alpha (PGF2 alpha), has been purified 232-fold from human uterine decidua vera. The molecular mass of the enzyme, as estimated by fast protein liquid chromatography, was 29 kDa. Sodium dodecyl sulfate disc gel electrophoresis of the denatured enzyme revealed a molecular mass of 31 kDa. These data suggest that the enzyme consists of a single polypeptide chain. The rate equation of the enzyme reaction for two substrates was used for the determination of five kinetic constants. The equilibrium constant with respect to PGE2 was 83 microM, the Michaelis constant, Km, for PGE2 was 93 microM. For NADPH, the equilibrium constant was 1.0 microM and Km was 1.6 microM. The maximal velocity for the forward reaction was V1 = 217 pmol/min. The inhibition constants for the analgesic agents indomethacin and fentiazac were Ki = 850 microM and Ki = 450 microM and for the steroid progesterone Ki = 1.5 mM, respectively. Prostaglandin-E2 9-ketoreductase might be responsible for the control of the PGE2/PGF2 alpha ratio in human decidua vera. The enzyme, therefore, might be an important factor in the cascade of events leading to uterine contractions and parturition.     

The extracellular matrix proteins laminin and fibronectin modify the AMPase activity of 5'-nucleotidase from chicken gizzard smooth muscle

Laminin and fibronectin, but not collagen, affect the AMPase activity of the purified transmembrane protein 5'-nucleotidase. Laminin stimulates whereas fibronectin inhibits the AMPase activity of this ectoenzyme. The AMPase-modulating effects by these components of the extracellular matrix require a preincubation period of several hours when detergent-solubilized 5'-nucleotidase is employed, they can, however, instantaneously be elicited with liposome-incorporated 5'-nucleotidase.     

Control of protein synthesis by amino acid supply. The effect of asparagine deprivation on the translation of messenger RNA in reticulocyte lysates

The enzyme asparaginase, which hydrolyses asparagine to aspartic acid, inhibited cell-free protein synthesis by reticulocyte lysates. The inhibition was rapid and complete when sufficient enzyme was added but could be prevented or reversed by the addition of asparagine. The initial effect of asparaginase appears to be a block in polypeptide chain elongation due to asparagine deprivation, but there are some indications that prolonged incubation under these conditions may give rise to a secondary decrease in initiation of protein synthesis.     

The Genetics of the DORSAL-BICAUDAL-D Region of DROSOPHILA MELANOGASTER

The chromosomal region 36C on 2L contains two maternal-effect loci, dorsal (dl) and Bicaudal-D (Bic-D), which are involved in establishing polarity of the Drosophila embryo along the dorsal-ventral and anterior-posterior axes, respectively. To analyze the region genetically, we isolated X-ray-induced dorsal alleles, which we recognized by virtue of the haplo-insufficient temperature-sensitive dorsal-dominant phenotype in progeny of single females heterozygous for a mutagenized chromosome. From the 20,000 chromosomes tested, we isolated three deficiencies, two inversions with breakpoint in dl and one apparent dl point mutant. One of the deficiencies, Df(2L)H20 (36A6,7; 36F1,2) was used to screen for EMS-induced lethal- and maternal-effect mutants mapping in the vicinity of dl and Bic-D. We isolated 44 lethal mutations defining 11 complementation groups. We also recovered as maternal-effect mutations four dl alleles, as well as six alleles of quail and one allele of kelch, two previously identified maternal-effect genes. Through complementation tests with various viable mutants and deficiencies in the region, a total of 18 loci were identified in an interval of about 30 cytologically visible bands. The region was subdivided into seven subregions by deficiency breakpoints. One lethal complementation group as well as the two maternal loci, Bic-D and quail, are located in the same deficiency interval as is dl.     

Prolonged plasma half-life of insulin in patients with a genetic defect of high affinity binding sites

Plasma clearance of endogenous and intravenously administered insulin was studied in three sibs with severe insulin resistance secondary to an affinity defect of their insulin receptors, and in five healthy controls. Intravenous infusion of somatostatin was used to inhibit the insulin secretion. 0.3 U of insulin/kg body weight was administered as an intravenous bolus. Plasma glucose, immunoreactive insulin and C-peptide were determined subsequently at constant intervals. We found a prolonged plasma half-life of insulin in the three patients, being 33.5 +/- 11.8 min vs 8.2 +/- 2.2 min in controls, P less than 0.002, but a normal half-life of C-peptide. The result indicates, that the plasma insulin clearance is predominantly mediated by intact insulin receptors. We conclude, that insulin has a prolonged half-life in all patients with insulin resistance secondary to an impaired receptor function.     

Portal vein network around the liver lobules demonstrates the lobular structure of the liver

The regularity of a basketlike surrounding of parenchymatous parts of the liver by portal branches proves the lobular organization of the liver. The wall formation of the portal basket (corbicula portalis) is demonstrated by several figures.