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Biomedical subjects

T B Ng

Publications and source records attributed to T B Ng.

At least 19 recordsLinked to original sources
PubMed1992

Growth hormone binding sites in tilapia (Oreochromis mossambicus) liver.

125I-labeled bovine and tilapia growth hormones were used to assess the presence of growth hormone receptors in membranes prepared from tissues of the tilapia Oreochromis mossambicus. The highest level of specific binding was detected in liver membranes from animals of both sexes and the binding was protein-dependent. Tilapia growth hormone, bovine growth hormone, and ovine prolactin, but not tilapia prolactin, potently inhibited the hepatic binding of 125I-labeled bovine growth hormone. Scatchard analysis of the 125I-labeled bovine growth hormone binding data revealed a Bmax (maximum binding) value of 180 fmol/mg protein and a Kd (dissociation constant) value of 13 nM. Tilapia growth hormone potently inhibited hepatic binding of 125I-labeled tilapia growth hormone. Scatchard analysis revealed a single class of binding sites with Bmax and Kd values of 390 fmol/mg protein and 2.5 nM, respectively. Bovine growth hormone and ovine prolactin were less potent while tilapia prolactin was inactive in inhibiting hepatic 125I-labeled tilapia growth hormone binding.

Animals↗
PubMed1992

Substances with alpha-melanotropin-like immunoreactivity in bovine brains.

1. Bovine cerebral hemispheres were extracted with an acidic medium (acetone-water-hydrochloric acid mixture, 40:5:1 by volume, pH 1.8). The precipitate which formed upon addition of a copious volume of cold acetone to the extract was designated acid acetone powder (AAP). 2. The AAP was then subjected to ion exchange chromatography on carboxymethyl (CM)-cellulose, gel filtration on Sephadex G100 and Sephadex G25, second ion exchange chromatography on CM-cellulose and high performance liquid chromatography. The absorbance of all fractions was measured at 280 nm and their alpha-melanotropin-(alpha-MSH)-like immunoreactivity was monitored with radioimmunoassay. 3. It was found that alpha-MSH-like immunoreactivity and bioactivity (lipolytic activity) was due to low molecular weight materials as evidenced by their retardation on Sephadex G-100 and Sephadex G-25. The immunoreactivity was distributed among fractions adsorbed and fractions unadsorbed on CM-cellulose and also among high performance liquid chromatographic fractions signifying the presence of multiple alpha-MSH-like molecules.

Animals↗
PubMed1992

beta-Momorcharin, a plant glycoprotein, inhibits synthesis of macromolecules in embryos, splenocytes and tumor cells.

1. beta-Momorcharin, a glycoprotein isolated from seeds of the bitter gourd, inhibited incorporation of [3H]leucine, [3H]uridine and [3H]thymidine into trichloroacetic acid-precipitable radioactivity in peri-implantation mouse embryos, mouse splenocytes with or without activation by concanavalin A, and human squamous carcinoma of the tongue and larynx, but did not affect incorporation of the aforementioned radioisotopes into mouse liver cells. 2. The results suggest that inhibition of protein, RNA and DNA biosynthesis in embryos, splenocytes and tumor cells may represent the mechanism of embryotoxic, immunosuppressive and antitumor actions of beta-momorcharin. 3. The results also suggest that in mouse liver cells biosynthesis of protein, RNA and DNA was not affected by beta-momorcharin.

Abortifacient Agents, Nonsteroidal↗
PubMed1992

Proteins with abortifacient, ribosome inactivating, immunomodulatory, antitumor and anti-AIDS activities from Cucurbitaceae plants.

1. The biochemical characteristics and biological activities of eight Cucurbitaceae plant proteins designated trichosanthin (isolated from tubers of Trichosanthes kirilowii), beta-trichosanthin (isolated from tubers of Trichosanthes cucumeroides), alpha- and beta-momorcharins (isolated from seeds of Momordica charantia), momorchochin (isolated from tubers of Momordica cochinchinensis), luffaculin (isolated from seeds of Luffa acutangula) and luffin-a and luffin-b (isolated from seeds of Luffa cylindrica), were reviewed. 2. The isolation procedures for all eight proteins are based on aqueous extraction, acetone fractionation and ion exchange chromatography. Ammonium sulfate precipitation and gel filtration are steps which may be included to improve purification. 3. The proteins are basic in nature and possess a molecular weight of approx. 30,000. All except trichosanthin are glycoproteins. The content of Asx and Glx residues is high. The N-terminal amino acid residue is Asp. Their amino acid compositions and N-terminal amino acid sequences are similar. 4. Circular dichroism spectroscopic studies revealed that trichosanthin, alpha- and beta-momorcharins possess similar secondary but different tertiary structures. 5. Most of the proteins are immunologically distinct. 6. The proteins exhibit abortifacient, antitumor, ribosome inactivating and immunomodulatory activities. Trichosanthin manifests anti-human immunodeficiency virus activity.

Abortifacient Agents↗
PubMed1992

High level synthesis of biologically active recombinant trichosanthin in Escherichia coli.

Two forms of recombinant trichosanthin (rTCS) were synthesized in high levels in Escherichia coli by putting the TCS cDNA under the control of a T7 RNA polymerase-directed promoter. Purification schemes were developed to isolate the recombinant protein from both soluble and insoluble fractions. Form I rTCS possessed the mature TCS sequence and had similar biological activities as the natural protein. Its IC50 was approximately 0.13 nM in an in vitro rabbit reticulocyte translational system and a dose of around 35 micrograms protein per 25 g body weight was sufficient to induce complete abortion in mice. Form II rTCS had a propeptide of 19 aa at the C-terminus and was five times less active than Form I in inhibiting protein synthesis by a rabbit reticulocyte lysate.

Abortifacient Agents↗
PubMed1992

Gonadotropin bioactivities in mouse, hamster, rat and guinea pig pituitaries are largely adsorbed on concanavalin A-sepharose.

The pituitaries of mice, hamsters, guinea pigs and rats were extracted with Tris-Cl buffer and the extracts were chromatographed on Concanavalin A (ConA)-Sepharose into unadsorbed ConA I and adsorbed ConA II fractions. The ConA I fraction was subjected to gel filtration on Sephadex G-100 and fractionated into an unretarded peak and several retarded peaks. The peak with a molecular weight of approximately 40,000 (designated ConAI Sephadex fraction II) was then subjected to ion exchange chromatography on CM-cellulose and fractionated into an unadsorbed CM I and an adsorbed CM II fraction. The ConA II fraction was fractionated by ion exchange chromatography on CM-cellulose into CM I and CM II fractions. The ConA II CM II fraction was the chromatographic fraction which exhibited the highest potency in stimulating testosterone production by isolated rat Leydig cells. Its activity was much higher than the corresponding ConA I Sephadex fraction II CM II fraction which differed chromatographically only by non-adsorption on ConA-Sepharose. The ConA II CM II fraction manifested cross reactivity in a rat luteinizing hormone (LH) radioimmunoassay. The guinea pig pituitary ConA II CM II fraction also cross-reacted in a rat thyroid stimulating hormone radioimmunoassay. The ConA II fractions of hamster and guinea pig pituitary extracts demonstrated follicle stimulating hormone (FSH) activity while the corresponding ConA I fractions did not. The results suggest that the ConA II/ConA II CM II fraction contained most of the FSH and LH activities present in the pituitary extract.

Animals↗
PubMed1992

The sea bream liver contains receptors for growth hormone and prolactin.

Different tissues of the black sea bream Mylio macrocephalus including the liver, gills, intestine, muscle, gonad, swim bladder, spleen, heart and kidney were examined for the presence of prolactin and growth hormone receptors. Membranes were prepared from the tissues and 125I-labeled ovine prolactin and bovine growth hormone were used as ligands. It was found that the liver contained the highest level of specific 125I-labeled ovine prolactin and bovine growth hormone binding, suggesting the existence of hepatic prolactin and growth hormone receptors. The protein nature of the hepatic growth hormone receptor was revealed by the reduction of specific 125I-labeled growth hormone binding after treatment of hepatic membranes with trypsin and chymotrypsin.

Animals↗
PubMed1992

Characterization of Mirabilis antiviral protein--a ribosome inactivating protein from Mirabilis jalapa L.

A protein was purified from root tubers of Mirabilis jalapa to homogeneity by ion-exchange chromatography on CM-Sepharose CL-6B and FPLC on Mono-S column. The purified protein was confirmed to be Mirabilis antiviral protein (MAP). However, in addition to its antiviral property, the MAP was demonstrated to possess abortifacient activity in pregnant mice, inhibitory effect on cell-free protein synthesis and antiproliferative effect on tumor cells. As judged from its biological and physiochemical properties, MAP is a type I ribosome-inactivating protein.

Abortifacient Agents↗
PubMed1992

Two proteins with ribosome-inactivating, cytotoxic and abortifacient activities from seeds of Luffa cylindrica roem (Cucurbitaceae).

Two immunologically distinct glycoproteins, with a molecular weight of 28,000 and 28,500 respectively, were isolated from seeds of Luffa cylindrica using a procedure that involved acetone precipitation, gel filtration on Sephadex G-75 and ion exchange chromatography on CM-Sepharose CL-6B. The proteins differed in the content of aspartic acid, threonine, proline and alanine but were otherwise similar in amino acid composition. The proteins were capable of inducing mid-term abortion in mice, inhibiting protein synthesis in a cell-free system and suppressing thymidine uptake by human choriocarcinoma cells.

Abortifacient Agents, Nonsteroidal↗
PubMed1991

Cloning of the cDNA of alpha-momorcharin: a ribosome inactivating protein.

Using a lambda gt11 cDNA library constructed from the seeds of the bitter melon (Momordica charantia), we have obtained a full length cDNA containing the entire sequence of alpha-momorcharin by immunoscreening. The length of this cDNA is 1044 basepairs long and it consists of an open reading frame coding for a polypeptide of 286 amino acids. The first 23 residues of this polypeptide probably code for a signal sequence. The N-terminal sequence of the deduced protein is exactly identical to that determined by peptide sequencing. The sequence identity between alpha-momorcharin and other ribosome inactivating proteins, such as trichosanthin and ricin A chain, is high, i.e., 34-63%. Examination of the predicted secondary structure of alpha-momorcharin and trichosanthin indicates that these proteins have regions of high structural similarities and this may account for the common biological activities that they share, viz., abortificant, immunosuppressive, antitumor and inhibition of HIV-1.

Amino Acid Sequence↗
PubMed1991

Cloning of trichosanthin cDNA and its expression in Escherichia coli.

Several cDNA clones coding for trichosanthin (TCS) have been isolated from a cDNA library prepared from the poly(A)+RNA of the root tuber of Trichosanthes kirilowii Maximowicz. The nucleotide sequence codes for a protein of 289 amino acids (aa) including a putative signal peptide of 23 aa and an extra 19 aa at the C terminus; the latter two have not been found in TCS obtained from the natural product [Collins et al., J. Biol. Chem. 265 (1990) 8665-8669]. Recombinant TCS (reTCS) was synthesized in Escherichia coli, in which the cDNA without the signal sequence was expressed under the control of the trc promoter; reTCS was detected by a rabbit anti-TCS antiserum.

Amino Acid Sequence↗
PubMed1991

Effect of methimazole-induced hypothyroidism on alveolar macrophages.

Chemically induced hypothyroidism changes the functions of rat alveolar macrophages. Treatment of female rats with an anti-thyroid drug, methimazole (1% aqueous solution in drinking water for 6 weeks) significantly (p less than 0.05) reduced the ability of alveolar macrophages (MAM) to phagocytose and kill the yeast, Saccharomyces cerevisiae. Undigested yeasts were observed in phagolysosomes within MAM using transmission electron microscopy. The activities of the lysosomal enzymes, acid phosphatase and beta-glucuronidase, and the Fc receptor binding ability for immunoglobulin G, were lowered in MAM when compared with control macrophages (CAM). MAM also produced less tumor necrosis factor under the stimulation of lipopolysaccharide.

Acid Phosphatase↗
PubMed1991

Presence of prolactin receptors in eel liver and carp kidney and growth hormone receptor in eel liver.

1. 125I-labelled ovine prolactin and bovine growth hormone were used to test for the presence of prolactin and growth hormone receptors in membrane prepared from tissues of the white eel Anguilla japonica, the carp Ctenopharynogodon idellus and the ricefield eel Monopterus albus. 2. High levels of specific 125I-labelled ovine prolactin binding were found in white eel liver membranes and carp kidney membranes. 3. High levels of specific 125I-labelled bovine growth hormone binding were detected in white eel liver membranes. 4. Tissues of the ricefield eel did not bind 125I-labelled ovine prolactin or bovine growth hormone. 5. The results suggest the presence of prolactin receptors in white eel liver and carp kidney membranes and growth hormone receptors in white eel liver membranes.

Animals↗
PubMed1991

Metabolic effects of bovine growth hormone in the tilapia Oreochromis mossambicus.

1. Bovine growth hormone (bGH) was injected into tilapia intramuscularly at a dose of 50 micrograms/100 g/day for a total of five injections. Control fish received saline instead. 2. The serum concentrations of amino acid and glucose were significantly higher and hepatic glycogen concentration and glycogen synthetase activity significantly lower in the bGH-treated fish than those in the control fish. 3. The serum concentrations of protein, lipid and cholesterol, and the hepatic concentrations of protein and lipid, remained unaltered after bGH treatment. 4. The results suggest that bGH exerts anti-insulin effects in tilapia.

Animals↗
PubMed1991

Trichosanthin induces atresia of ovarian follicles and inhibits steroidogenesis in gonadotropin-primed immature mice.

1. Immature mice were induced to ovulate by injections of pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin spaced 48 hr apart. 2. Trichosanthin (TCS), a protein purified from tubers of Trichosanthes kirilowii (Family Cucurbitaceae), was administered respectively 24 hr before, on the same day as, 24 hr after and 48 hr after the PMSG injection. 3. The results of TCS injections at different times were generally similar. The number of maturing follicles, corpora lutea and ovulated oocytes, and the ovarian weight, remained unaltered. 4. However, there was an increased incidence of follicular atresia and degeneration of ovulated oocytes, and a lowering of serum estradiol-17 beta and progesterone levels.

Animals↗
PubMed1991

Isolation of a ribosome-inactivating and abortifacient protein from seeds of Luffa acutangula.

A glycoprotein with a molecular weight of 28,000 as estimated by SDS-polyacrylamide gel electrophoresis was isolated from seeds of Luffa acutangula using a procedure that involved acetone precipitation, ion exchange chromatography on CM Sepharose CL-6B and gel filtration on Sephadex G-50. In immunodiffusion studies it was found to be immunologically distinct from abortifacient proteins isolated from other members of the Cucurbitaceae family including Momordica charantia, Momordica cochinchinensis, Trichosanthes kirilowii and Trichosanthes cucumeroides. There were some differences in amino acid composition among the proteins although there was a gross similarity. The protein from L. acutangula was capable of inducing mid-term abortion in mice and inhibiting protein synthesis in a cell-free system.

Abortifacient Agents↗
PubMed1991

Studies on tilapia hepatic growth hormone receptor.

Tilapia liver membranes were solubilized with 1% Triton X-100. The presence of growth hormone (GH) receptors was demonstrated by specific binding of radioiodinated tilapia GH (125I-tGH). The solubilized receptor possessed a molecular weight of around 400,000. It was adsorbed on Con A-Sepharose and DEAE BioGel A indicating that it contains carbohydrates and is acidic in character. Its protein nature was revealed by destruction of GH-binding activity by proteases. The involvement of essential sulfhydryl group was suggested by inhibition of 125I-tGH binding to the solubilized receptor by p-chloromercuribenzene sulfonate which could be reversed by dithioerythritol treatment.

4-Chloromercuribenzenesulfonate↗