Role of luteinizing hormone-releasing factor (LH-RF) and LH on maintenance of early gestation in rats.

The role of luteinizing hormone (LH) and LH-releasing hormone (LH-RH) in the maintenance of early pregnancy in rats was studied. Serum levels of progesterone (P) and LH were measured daily in untreated pregnant rats from Day 4 through parturition. Serum levels of P and LH were determined on Days 11 and 15 of pregnancy in animals treated with antisera to LH (LH-A/S) and to LH-RH (LH-RH-A/S) on Days 8-10. Serum levels of P peaked on Days 7 and 16 in untreated animals, after which they declined sharply just before delivery. Serum LH fluctuated between 30-160 ng/ml during pregnancy but did not exhibit any distinctive peaks. Treatment with .2 ml LH-A/S on Days 8-10 reduced serum P to virtually undetectable levels on Day 11, and only a slight recovery was evident on Day 15. Lower doses of LH-A/S had no effect. Administration of 1.3 ml LH-RH-A/S had no effect on serum levels of P or LH, and did not impede fetal development. The results indicate that LH is essential to the luteotropic complex of early pregnancy in the rat, and also that LH-RH-A/S can maintain to some extent basal levels of P and LH during early pregnancy.     

Properties of membrane-bound α-glucosidases: Possible sugar receptor protein of the blowfly, Phormia regina

Previously reported PII-type α-glucosidase located in the precipitate of the labellar homogenate of the blowfly Phormia regina was solubilized by sodium deoxycholate (DOC) and further separated into three isozymes with different molecular weight: PII-M (mol. wt 9 × 10⁴). PII-D (mol. wt 2 × 10⁵) and PII-T (mol. wt 8 × 10⁵) by molecular sieve chromatography on Biogel P-300 or Ultragel AcA-34. These three isozymes had almost the same K_m's and relative values of V_m's for several substrates, suggesting that they had the same common active site.PII-D and PII-T are more strongly embedded in the membrane than PII-M, because the proportion of PII-D and PII-T was much increased when the remaining glucosidase in the precipitate after the first solubilization was reextracted by DOC. A large peak of α-glucosidase isozyme P-IV which preferentially hydrolyze sucrose eluted just after P-II (soluble P-II) when the supernatant fraction of the labellar homogenate was chromatographed on DEAE-Sephadex A-50. P-IV was scarcely present in the precipitate fraction.Soluble P-II had the same mol. wt as PII-M and had similar properties to PII-M except for the ratio of V_m's.A large proportion of PII-D was contained in the well washed labellar integuments, a preparation rich in labellar chemosensilla. It suggests that most of the insoluble α-glucosidase contained in the dendrite in labellar chemosensilla is PII-D. PII-D (and PII-T) are possible sites of the pyranose receptor molecule because their properties and localization agree well with those of the receptor.     

Flavonoids isolated from the leaves of Melicope triphylla and their extracellular-superoxide dismutase-inducing activity

Two novel flavonoids, named meliflavones A (1) and B (2), were isolated from the leaves of Melicope triphylla (Lam.) Merr., along with thirteen known compounds (3–15). Four of the polymethoxyflavonoids bearing a prenyloxy (3-methylbut-2-enyloxy) function (1, 3–5) induced the expression of extracellular-superoxide dismutase (EC-SOD) in a human leukemic U937 cell-based assay.     

A novel cyanobacterial SmtB/ArsR family repressor regulates the expression of a CPx-ATPase and a metallothionein in response to both Cu(I)/Ag(I) and Zn(II)/Cd(II)

A novel SmtB/ArsR family metalloregulator, denoted BxmR, has been identified and characterized from the cyanobacterium Oscillatoria brevis. Genetic and biochemical evidence reveals that BxmR represses the expression of both bxa1, encoding a CPx-ATPase metal transporter, as well as a divergently transcribed operon encoding bxmR and bmtA, a heavy metal sequestering metallothionein. Derepression of the expression of all three genes is mediated by both monovalent (Ag(I) and Cu(I)) and divalent (Zn(II) and Cd(II)) heavy metal ions, a novel property among SmtB/ArsR metal sensors. Electrophoretic gel mobility shift experiments reveal that apoBxmR forms multiple resolvable complexes with oligonucleotides containing a single 12-2-12 inverted repeat derived from one of the two operator/promoter regions with similar apparent affinities. Preincubation with either monovalent or divalent metal ions induces disassembly of both the BxmR-bxa1 and BxmR-bxmR/bmtA operator/promoter complexes. Interestingly, the temporal regulation of expression of bxa1 and bmtA mRNAs is different in O. brevis with bxa1 induced first upon heavy metal treatment, followed by bmtA/bxmR. A dynamic interplay among Bxa1, BmtA, and BxmR is proposed that maintains metal homeostasis in O. brevis by balancing the relative rates of metal storage and efflux of multiple heavy metal ions.     

GTP and GDP will stimulate platelet cytosolic phospholipase C independently of Ca2+

The hydrolysis of [3H]phosphatidylinositol 4,5-bisphosphate (PIP2) by cytosolic phospholipase C from human platelets was determined. Cytosolic fractions were prepared from platelets that had or had not been preactivated with thrombin. Thrombin pretreatment did not affect cytosolic phospholipase C activity. In both cytosolic fractions, phospholipase C was activated by GTP and GTP gamma S. This action is observed in the presence of 2 mM EGTA. GDP was as effective as GTP in stimulating cytosolic phospholipase C in the presence of Ca2+ or EGTA. Partially purified phospholipase C obtained from platelet cytosol is activated by GTP, but not by GTP gamma S, in the presence of 2 mM EGTA. However, in the presence of 6 microM Ca2+, both GTP and GTP gamma S stimulated the partially purified phospholipase C. Our present information indicates that GTP and GDP have a direct effect on the cytosolic phospholipase C.     

Inhibition of cell growth and induction of apoptotic cell death by the human tumor-associated antigen RCAS1.

Tumor-associated antigens that can be recognized by the immune system include the MAGE-family, p53, MUC-1, HER2/neu and p21ras. Despite their expression of these distinct antigens, tumor elimination by the immune system is often inefficient. Postulated mechanisms include insufficient expression of co-stimulatory or adhesion molecules by tumor cells, or defective processing and presentation of antigens on their cell surfaces. Tumor cells may also evade immune attack by expressing CD95 (APO-1/Fas) ligand or other molecules that induce apoptosis in activated T cells. Here we describe RCAS1 (receptor-binding cancer antigen expressed on SiSo cells), a membrane molecule expressed on human cancer cells. RCAS1 acts as a ligand for a putative receptor present on various human cell lines and normal peripheral lymphocytes such as T, B and NK cells. The receptor expression was enhanced by activation of the lymphocytes. RCAS1 inhibited the in vitro growth of receptor-expressing cells and induced apoptotic cell death. Given these results, tumor cells may evade immune surveillance by expression of RCAS1, which would suppress clonal expansion and induce apoptosis in RCAS1 receptor-positive immune cells.     

Synthesis of N-chlorosulfonyl dicyclohexylamine as a potent inhibitor for spermidine synthase and its effects on human leukemia Molt4B cells

N-Chlorosulfonyl dicyclohexylamine (CSD) was synthesized as a potent inhibitor of spermidine synthase and analyzed for antiproliferative effects on leukemic cells. The compound specifically inhibited spermidine synthase in a competitive mode with the substrate putrescine (Ki, 1.8 X 10(-7) M). When human leukemia Molt4B cells were cultured in the presence of the inhibitor, the intracellular level of spermidine and the rate of cell proliferation were markedly depressed. In these polyamine depleted and growth retarded cells the synthesis of protein, but not of DNA or RNA, was found to be significantly diminished.     

Seasonal N uptake and N2fixation by common and adzuki bean at various spacings

The adzuki bean (Vigna angularis (Wild.) Ohwi and Ohashi) and common bean (Phaseolus vulgaris L.) have a high physiological demand for N. A 2-year field study was conducted to investigate the seasonal change of available soil N and symbiotic N₂ fixation usage. The beans were seeded at two densities, 22.2 plants m^–2 with a row spacing of 0.3 m and 11.1 plants m^–2 with a row spacing of 0.6 m. The amount of fixed N₂ in the shoot was calculated using the ¹⁵N natural abundance method. The common bean demonstrated low N₂ fixation and the ability to accumulate high levels of soil N. Soil nitrate under the common bean was continually absorbed. The adzuki bean, on the other hand, had a remarkable peak of N accumulation in the early reproductive stage. This was mainly due to N₂ fixation, though the soil nitrate level was high. Narrowing the plant row spacing increased the dry matter yield of both species, but the origin of the increased N differed between the species. For the first 77 DAP in 1999 (73 DAP in 2000) the N increase for both beans was due to both soil and atmospheric N₂. At harvest, though, the increase of N in common bean was mainly due to soil N, while that in adzuki bean was mainly due to atmospheric N₂. It can be concluded that the low symbiotic N₂ fixation ability of common bean was due to its high soil N uptake ability and constant N accumulation, which enabled an efficient soil N absorption. Adzuki bean absorbed N mainly for a short period and depended more on symbiotically fixed N₂ and, in contrast to common bean, left a high level of NO₃-N remaining in the soil after cropping.