Biosynthesis of Alkali Insoluble Polysaccharide from UDP-d-Glucose with Particulate Enzyme Preparations from Phaseolus aureus

A particulate enzyme system from Phaseolus aureus seedlings catalyzes the synthesis of alkali insoluble polysaccharide material from UDP-d-glucose. 80 to 90% of the d-glucose units are joined by β-1,4 linkages, the remainder being combined by β-1,3 linkages. It is not known whether the material is a single polysaccharide or a mixture.     

Differences of Ca2+ regulation in skin fibroblasts from blacks and whites

Black people have a higher propensity than caucasians toward essential hypertension. To explore the possibility that this racial difference relates to cellular Ca2+ metabolism, we measured 45Ca2+ washout and uptake and cytosolic free concentration of Ca2+ [Ca2+]i in serially passed skin fibroblasts from normotensive black and white males. Depending on the experimental conditions, 45Ca2+ washout in these cells was described by either two or three exponential functions, whereas 45Ca2+ uptake was described only by a two-exponent function. There were no racial differences in 45Ca2+ uptake and washout of unstimulated fibroblasts. However, stimulation by human serum resulted in an increase in the 45Ca2+ washout that was higher in fibroblasts from blacks than from whites. The racial differences were expressed primarily by higher values of the apparent washout rate constant (k1) of 45Ca2+ from the largest and most rapidly exchangeable cellular pool. The effect of human serum was not related to its origin (blacks vs. whites). In 2 mM Ca2+ medium and 10% serum from blacks, the respective k1 (mean +/- SEM; x 10(-2)/min) values for fibroblasts from blacks and whites were 89.68 +/- 5.23 and 73.29 +/- 4.0; in the presence of 10% serum from whites, the k1 values for cells from blacks and whites were 84.14 +/- 2.80 and 76.36 +/- 3.23 (overall significance of P less than .01). In Ca2+-deficient medium in the presence of 10% human serum, the k1 for fibroblasts from blacks and whites were 115.57 +/- 3.76 and 102.15 +/- 3.30 (P less than .05). Serum substantially increased the 45Ca2+ uptake in fibroblasts from both blacks and whites; however, racial differences were not observed. Basal levels of [Ca2+]i were not different in fibroblasts of blacks vs. whites (46.8 +/- 6.8 and 43.2 +/- 7.1 nM for blacks and whites, respectively). However, the peak response of Cai2+ transients for cell stimulated by 5% human serum was significantly higher in blacks than whites (blacks = 963 +/- 213, whites = 481 +/- 162 nM; P = .0286). We conclude that Ca2+ regulation is different in serum-stimulated fibroblasts from blacks and whites and that, at least in part, this difference may relate to a greater agonist-induced mobilization of Ca2+ in fibroblasts from blacks.     

Effect of Inhibitors on the Formation of Stereoisomers in the Biosynthesis of {beta}-Carotene in Dunaliella bardawil

An assay system was developed in which the effects of inhibitorsof ß-carotene biosynthesis in Dunaliella bardawilcould be tested. Since D. bardawil can be induced to accumulateover 10% of its dry weight as ß-carotene, it is particularlysuitable for such studies. Norflurazon a desaturation inhibitor,caused the accumulation of phytoene, or of phytoene and phytofluene,depending on the concentration employed. J-334, a substituted6-methylpyrimidine which also inhibits desaturation, causedthe accumulation of ß-zeacarotene, -carotene and phytoenein different proportions, depending on the concentration employed.The cyclization inhibitors, nicotine, CPTA and MPTA, severelyaffected the growth and survival of the alga, and their effectscould therefore not be studied directly. However, their actionwas observed indirectly by following the transformation of phytoenein norflurazon-pretreated phytoene-rich algae. Under these conditions,presence of the cyclase inhibitors caused the transformationof phytoene to lycopene, rather than to ß-carotene.The accumulated ß-carotene or the intermediates ß-zeacarotene,lycopene, -carotene, phytofluene and phytoene in D. bardawilwere all composed of two stereoisomers, tentatively assignedas the all-trans stereoisomer (55%) and the 9-cis stereoisomer(45%). This suggests that the isomerization reaction which leadsto the production of the presumed 9-cis isomers occurs earlyin the pathway of carotene biosynthesis, at or before phytoene,with no isomerization during the further transformations leadingto ß-carotene. (Received January 29, 1990; Accepted May 9, 1990)     

Are active oxygen species involved in induction of β-carotene in Dunaliella bardawil?

The purpose of this work was to test whether induction of massive -carotene synthesis in the alga Dunaliella bardawil is triggered by oxygen radicals. The following results were obtained: (i) The induction of -carotene synthesis is preceded by a lag period of about 4 h during which the cells swell and photosynthesis is partially inhibited, (ii) Addition of promoters of oxygen radicals or of azide (an inhibitor of catalase and superoxide dismutase) during the induction period, under conditions which are suboptimal for massive -carotene accumulation, greatly enhances -carotene synthesis, photodegradation of chlorophyll and inhibition of photosynthesis, (iii) High irradiance, which induces massive -carotene accumulation, also induces a high catalase activity. It is suggested that photosynthetically produced oxygen radicals are involved in triggering massive -carotene accumulation in D. bardawil.     

Reduction in animal abundance and oxygen availability during and after the end-Triassic mass extinction

The end-Triassic biodiversity crisis was one of the most severe mass extinctions in the history of animal life. However, the extent to which the loss of taxonomic diversity was coupled with a reduction in organismal abundance remains to be quantified. Further, the temporal relationship between organismal abundance and local marine redox conditions is lacking in carbonate sections. To address these questions, we measured skeletal grain abundance in shallow-marine limestones by point counting 293 thin sections from four stratigraphic sections across the Triassic/Jurassic boundary in the Lombardy Basin and Apennine Platform of western Tethys. Skeletal abundance decreased abruptly across the Triassic/Jurassic boundary in all stratigraphic sections. The abundance of skeletal organisms remained low throughout the lower-middle Hettangian strata and began to rebound during the late Hettangian and early Sinemurian. A two-way ANOVA indicates that sample age (p < .01, η² = 0.30) explains more of the variation in skeletal abundance than the depositional environment or paleobathymetry (p < .01, η² = 0.15). Measured I/Ca ratios, a proxy for local shallow-marine redox conditions, show this same pattern with the lowest I/Ca ratios occurring in the early Hettangian. The close correspondence between oceanic water column oxygen levels and skeletal abundance indicates a connection between redox conditions and benthic organismal abundance across the Triassic/Jurassic boundary. These findings indicate that the end-Triassic mass extinction reduced not only the biodiversity but also the carrying capacity for skeletal organisms in early Hettangian ecosystems, adding to evidence that mass extinction of species generally leads to mass rarity among survivors.     

Generation of heteroplastidic Nicotiana cybrids by protoplast fusion: analysis for plastid recombinant types

Summary Protoplasts of a mutant line of Nicotiana tabacum having a maternally-transmitted chlorophyll deficiency were fused with protoplasts of two alloplasmic-male-sterile Nicotiana lines by the donor-recipient technique. In both fusion experiments variegated plantlets were regenerated which were shown to contain cytoplasms of mixed chloroplast nature. This confirms that with the donor-recipient method one can obtain mixed cytoplasms of genetically different chloroplasts. We present a convenient system to assay for genetic recombination between chloroplasts by combining use of several cytoplasmic markers: vis. chlorophyll pigmentation, chloroplast DNA restriction patterns, tentoxin resistance and male sterility. Within the limits of the experiment no recombinant types were recovered.     

Induction of fatty acid cyclooxygenase activity in canine kidney cells (MDCK) by benzo(a)pyrene.

Canine kidney cells (MDCK) in which [3H]arachidonic acid was esterified in the cellular lipids released increased levels of radioactive prostaglandins and arachidonic acid into the medium when cultured in the presence of benzo(a)pyrene. When MDCK cells were cultured in the presence of benzo(alpha)pyrene and 7,8-benzoflavone, this increased release was not observed. MDCK cells incubated with benzo(a)pyrene also converted exogenous arachidonic acid into prostaglandins more effectively than cells grown in its absence. 7,8-Benzoflavone inhibited this benzo(a)pyrene effect. Microsomes, prepared from benzo(alpha)pyrene-treated MDCK cells synthesized prostaglandin F2alpha from arachidonic acid more effectively than nontreated cells.     

Cloning of bovine growth hormone gene and its expression in bacteria.

A hybrid plasmid was constructed containing beta-lactamase gene of plasmid pBR322 and cloned coding sequences of bovine growth hormone (BGH). The constructed plasmid contains all DNA sequences required to encode BGH, and when used as a hybridization probe it detects one growth hormone gene in the bovine genome. The cloned DNA sequences are inserted into the beta-lactamase gene in the correct reading frame for BGH synthesis. The hybrid gene is expressed in bacteria and the product, a fused beta-lactamase-bovine growth hormone protein, is specifically immunoprecipitated with anti-serum to BGH. Unlike beta-lactamase, very little growth hormone containing sequences can be detected in the periplasmic space.