Gonadotropin releasing hormone in first trimester human placenta: Isolation,partial characterisation andin vitro biosynthesis

Using a specific radioimmunoassay for gonadotropin releasing hormone, the presence of gonadotropin releasing hormone like material in the first trimester human placenta has been demonstrated. The material has been partially characterized using carboxy methyl cellulose chromatography, high pressure gel permeation chromatography and reverse phase C18 high pressure liquid chromatographic analysis. Analysis for bioactivity revealed that placental gonadotropin releasing hormone is much more active than synthetic gonadotropin releasing hormone inin vitro rat pituitary lutinising hormone release assay.In vitro biosynthetic studies using labelled precursors and immunoaffinity chromatography indicated that first trimester human placenta synthesizes gonadotropin releasing hormone like material.     

Ethylene biosynthesis in isolated vacuoles of Vicia faba L. — requirement for membrane integrity

The ability of vacuoles prepared from V. faba leaves to convert 1-aminocyclopropane-1-carboxylic acid to C₂H₄ was destroyed when vacuoles were lysed by passage through a hypodermic needle, freezing and thawing, osmotic shock, treatment with ethanol or with a detergent. Ethylene synthesis in the vacuolar fraction was also inhibited by the uncouplers carbonyl cyanide m-chlorophenyl hydrazone and dinitrophenol and by the ionophores valinomycin, nigericin, and A23187. Ethylene formation increased with increasing pH of the incubation medium over the pH range of 5.0–7.5. These observations support the hypothesis that C₂H₄ biosynthesis in vacuolar preparations is dependent on membrane integrity, possibly because of the requirement for a transmembrane ion gradient.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine - CCCP carbonyl cyanide m-chlorophenyl hydrazone     

The carotenoid and abscisic acid content of viviparous kernels and seedlings ofZea mays L.

Carotenoid and abscisic acid (ABA) levels were determined in endosperm, embryos and seedlings of wild-type and viviparous (vp) mutants ofZea mays L. Carotenoid concentrations were determined by absorption spectrometry following purification by high-performance liquid chromatography and ABA concentrations by combined gas chromatography-mass spectrometry. Lutein and zeaxanthin were the terminal carotenoids in wild-type tissue. The carotenoid profiles ofvp-1 andvp-8 tissue were similar to that of the wild type; invp-2, vp-5, vp-7 andvp-9 carotenogenesis was blocked at early stages so that xanthophylls were absent. Except forvp-1, where the ABA content was similar to the wild type, the ABA content ofvp embryos was substantially reduced, to 6–16% of the corresponding wild type. Thus, the absence of xanthophylls was associated with reduced ABA content, which was in turn correlated with vivipary. Kernels ofvp-8 had a reduced ABA content although xanthophylls were present. Seedlings of carotenoid-deficient mutants rescued from viviparous kernels contained less ABA than did wild-type seedlings grown in the same way. Furthermore, the ABA concentration of such seedlings did not increase in response to water deficit. Conversely,vp-1 seedlings contained normal levels of carotenoids and ABA. Carotenoid-deficient seedlings did not contain appreciable amounts of chlorophyll so that chloroplast development was not normal. Thus ABA-deficiency could be associated with abnormal plastid development rather than the absence of carotenoids per se.Abbreviations ABA abscisic acid - DAP days after pollination - i.d. internal diameter - FW fresh weight - GC-MS combined gas chromatography-mass spectrometry - HPLC high-performance liquid chromatography - MS mass spectrometry - vp viviparous     

Metabolism of gibberellins in a cell-free system from immature seeds of Phaseolus vulgaris L.

The biosynthetic steps from gibberellin A₁₂-aldehyde (GA₁₂-aldehyde) to C₁₉-GAs were studied by means of a cell-free system from the embryos of immature Phaseolus vulgaris seeds. Stable-isotope-labeled GAs were used as substrates and the products were identified by gas chromatography-mass spectrometry. Gibberellin A₁₂-aldehyde was converted to GA₄ via non-hydroxylated intermediates and to GA₁ via 13-hydroxylated intermediates. 13-Hydroxylation took place at the beginning of the pathway by the conversion of GA₁₂-aldehyde to GA₅₃-aldehyde. The conversion of GA₂₀ to GA₅ and GA₆ was also shown but no 2-hydroxylating activity was found. Endogenous GAs from embryos and testas of 17-dold seeds were re-examined by gas chromatography-selected ion monitoring using stable-isotopelabeled GAs as internal standards. Gibberellins A₉, A₁₂, A₁₅, A₁₉, A₂₃, A₂₄, and A₅₃ were identified for the first time in P. vulgaris, in addition to GA₁, GA₄, GA₅, GA₆, GA₈, GA₁₇, GA₂₀, GA₂₉, GA₃₇, GA₃₈ and GA₄₄, which were previously known to occur in this species. The levels of all GAs, except the 2-hydroxylated ones, were greater in the embryos than in the testas. Conversely, the contents of GA₈ and GA₂₉, both 2-hydroxylated, were much higher in the testas than in the embryos.Abbreviations GA_n gibberellin A_n - GC-MS gas chromatography-mass spectrometry - GC-SIM gas chromatography-selected ion monitoring - HPLC high-performance liquid chromatography - TLC thin-layer chromatography - m/z ion of mass     

Feedback inhibition of homoserine kinase from radish leaves

Homoserine kinase is a potential control point in the biosynthetic pathway for threonine, isoleucine and methionine. The radish leaf enzyme was tested     

Distribution of carotenoids in sub-cellular and sub-plastidic fractions of radish seedlings (Raphanus sativus) grown in the presence of bleaching herbicides

The intracellular and intraplastidic distribution of carotenoids has been investigated in radish seedlings grown in the presence of the herbicides amitrole and SAN 6706. Both herbicides caused bleaching and the plants became deficient in chlorophylls and the usual chloroplast cyclic carotenoids, but accumulated the acyclic carotenoid biosynthetic intermediates 15-cis-phytoene and all-trans-lycopene. In both the untreated and herbicide-treated plants all carotenoids, including phytoene and lycopene, were contained in the plastid. In all cases the normal cyclic carotenoids were located virtually exclusively in the thylakoid or prothylakoid fraction. In amitrole-treated plants, lycopene also was contained only in the thylakoid fraction, whereas phytoene, in these and in SAN 6706-treated plants, was detected in both the thylakoid fraction and an envelope preparation. Possible implications for the biosynthesis of the carotenoids are discussed.     

The carotenoid pigments in the juice and flavedo of a mandarin hybrid (Citrus reticulata) cv michal during ripening

The carotenoid pigments ofthe mandarin hybrid (Citrus reticulata) cv Michal, in the juice and flavedo were characterized at three ripening stages, before, during and after colour break. During ripening the characteristic mandarin pattern was formed in the juice, which contained cryptoxanthin as the principal pigment. In the flavedo the chloroplast carotenoid pattern of the green fruit changed into the characteristic pattern of C. reticulata with a high level of citraurin which, together with cryptoxanthin, imparts an intensive reddish tint to the hybrid. The flavedo contained an unusual C₃₀ apocarotenoid, β-citraurinene (8′-apo-β-caroten-3-ol). The flavedo carotenoids of this accidental hybrid were compared with the carotenoids of the presumed parents Dancy tangerine and Clementine. The hybrid resembles more the second parent, from which it inherited the ability to biosynthesize a higher amount of citraurin as well as citraurinene. Citraurinene, considered a Citrus hybrid-specific pigment, was found for the first time in a Citrus variety. A possible biosynthetic pathway of the Citrus C₃₀ -apocarotenoids is proposed.     

Biosynthesis of lysosomal endopeptidases

Despite the clear differences between the amino acid sequence and enzymatic specificity of aspartic and cysteine endopeptidases, the biosynthetic processing of lysosomal members of these two families is very similar. With in vitro translation and pulse-chase analysis in tissue culture cells, the biosynthesis of cathepsin D, a aspartic protease, and cathepsins B, H and L, cysteine proteases, are compared. Both aspartic and cysteine endopeptidases undergo cotranslational cleavage of an amino-terminal signal peptide that mediates transport across the endoplasmic reticulum (ER) membrane. Addition of high-mannose carbohydrate also occurs cotranslationally in the lumen of the ER. Proteases of both enzyme classes are initially synthesized as inactive proenzymes possessing amino-terminal activation peptides. Removal of the propeptide generates an active single-chain enzyme. Whether the single-chain enzyme undergoes asymmetric cleavage into a light and a heavy chain appears to be cell type specific. Finally, late during their biosynthesis both classes of enzymes undergo amino acid trimming, losing a few amino acid residues at the cleavage site between the light and heavy chains and/or at their carboxyltermini. During biosynthesis these enzymes are also secreted to some extent. In most cells the secreted enzyme is the proenzyme bearing some complex carbohydrate. Under certain physiological conditions the inactive secreted enzymes may become activated as a result of a conformational change that may or may not result in autolysis. Analysis of the biochemical nature of the various processing steps helps define the cellular pathway followed by newly synthesized proteases targeted to the lysosome.     

Regulation of UDP-Galactose:Ceramide Galactosyltransferase and UDP-Glucose:Ceramide Glucosyltransferase After Crush and Transection Nerve Injury

The enzyme activities of ceramide galactosyltransferase and ceramide glucosyltransferase were assayed as a function of time (0, 1, 2, 4, 7, 14, 21, 28, and 35 days) after crush injury or permanent transection of the adult rat sciatic nerve. These experimental models of neuropathy are characterized by the presence and absence of axonal regeneration and subsequent myelin assembly. Within the first 4 days after both injuries, a 50% reduction of ceramide galactosyltransferase-specific activity was observed compared to values found in the normal adult nerve. This activity remained unchanged at 7 days after injury; however, by 14 days the ceramide galactosyltransferase activity diverged in the two models. The activity increased in the crushed nerve and reached control values by 21 days, whereas a further decrease was observed in the transected nerve such that the activity was nearly immeasurable by 35 days. In contrast, the ceramide glucosyltransferase activity showed a rapid increase between 1 and 4 days, followed by a plateau that was 3.4-fold greater than that in the normal adult nerve, which persisted throughout the observation period in both the crush and transection models. [3H]Galactose precursor incorporation studies at 7, 14, 21, and 35 days after injury confirmed the previously observed shift in biosynthesis from the galactocerebrosides during myelin assembly in the crush model to the glucocerebrosides and oligohexosylceramide homologues in the absence of myelin assembly in the transection model. The transected nerves were characterized by a peak of biosynthesis of the glucocerebrosides at 14 days. Of particular interest is the biosynthesis of the glucocerebrosides and the oligohexosylceramides at 7 and 14 days after crush injury.(ABSTRACT TRUNCATED AT 250 WORDS)     

咖啡碱对椎实螺胚增长的影响

作者采用简单的螺胚生长抑制法,证明软体动物细胞具有DNA复制后修复功能,并受咖啡碱抑制。在没有其他诱变剂的参与下,咖啡碱并不损伤DNA,但也没有保护作用。