Plasma esterase activities in rats fed magnesium-deficient diets

In a study with rats it was determined whether dietary magnesium concentration affects plasma esterase activities. The feeding of a diet with 0.01% (w/w) instead of 0.04% magnesium reduced plasma magnesium concentration by 50%. Plasma total esterase, arylesterase and butyrylcholinesterase activities were significantly decreased in the magnesium-deficient rats. In rats fed a diet containing 0.02% magnesium, plasma magnesium concentration was lowered by 30%, and group mean plasma total esterase activity was decreased, but not the activities of arylesterase and butyrylcholinesterase.     

Exclusion cage studies on the impact of predation on Helicoverpa armigera in cotton

The impact of predation on Helicoverpa armigera was studied in four field cage exclusion trials on cotton in Kenya. H. armigera egg cohorts were introduced inside predator‐free and open control cages, and the impact of local predator populations on the cohort was examined. Fourteen days after inoculation, exclusion cages had four times more larvae than controls, indicating a strong impact of predation. Ants and Anthocoridae were the predominant predator groups. Exclusion cages had more damaged fruiting plant parts (squares, flowers and bolls) than the control. In the absence of predators, natural mortality of H. armigera was greater as cotton matured, and is likely to be linked to the host plant condition.     

-cyano-substituted analogoues of decarboxylated S-adenosylmethionine as enzyme activated, irreversible inhibitors of S-adenosylmethionine decarboxylase

A pair of -cyano analogues of decarboxylated S-adenosylmethionine (2a and 2b) were synthesized as potential enzyme activated, irreversible inhibitors of the[pyruvoyl enzyme S-adenosylmethionine decarboxylase (AdoMet-DC). Each of these analogues acts as an irreversible inactivator for ADoMet-DC from Escherichia coli (IC₅₀ values of 9 and 50 μM, respectively). These analogues also inactivate human AdoMet-DC, with K_I values of 246.6 and 7.2 μM, and k_inact values of 0.29 and 0.03 min⁻¹, respectively.     

Floral development and expression of floral homeotic genes are influenced by cytokinins

Tobacco plants that are somatic mosaics for the expression of a cytokinin-synthesizing gene have viviparous leaves. Epiphyllous buds can be either vegetative or floral. Floral adventitious buds can be either normal or abnormal. Abnormalities of floral development correlate with: (i) a local activation of the cytokinin-synthesizing gene, (ii) a drastic increase in floral cytokinin content, and (iii) a decrease in the steady-state levels of mRNA homologues of the homeotic genes DEFA , GLO and PLENA of Antirrhinum majus . Thus, these data show in planta that cytokinins, a class of phytohormones, are able to alter the development of floral organs and to decrease the expression of three homeotic floral genes.     

Inflorescence-specific genes from Arabidopsis thaliana encoding glycine-rich proteins

Genomic and cDNA clones for three inflorescence-specific genes from Arabidopsis thaliana were isolated and characterized. The genes are tandemly organized in the genome on a 10 kb fragment. The expression of these genes is coordinately regulated in a developmental and organ-specific pattern. They are expressed predominantly in anthers at the later stage of flower development. The primary structure of the encoded gene products exhibits comparable features consisting of a hydrophobic domain at the N-terminal region followed by repeated glycine-rich motifs. Little homology is observed either between the glycine-rich domain of the three genes or with previously described glycine-rich proteins from other plant species.     

Preparation of the pure diastereomeric forms of S- (5′-deoxy-5′-adenosyl)-1-ammonio-4-methylsulfonio-2- cyclopentene and their evaluation as irreversible inhibitors of S-adenosylmethionine decarboxylase from Escherichia coli

The conformationally restricted S-adenosylmethionine analogue AdoMac (S-(5′-deoxy-5′-adenosyl)-1-ammonio-4-methylsulfonio-2-cyclopentene has been shown to act as an enzyme activated, irreversible inhibitor of theEscherichia coli form of the enzyme S-adenosylmethionine decarboxylase. Inactivation of the enzyme is presumably initiated by formation of an imine linkage between the inhibitor and the terminal pyruvate of the enzyme, followed by base-catalyzed elimination of methylthioadenosine and generation of a latent electrophile. Removal of the driving force for the elimination of methylthioadenosine resulted in a reversibly binding inhibitor. Thus, the thioether analogue corresponding to AdoMac, and the corresponding dihydro derivative (H₂-AdoMac), reversibly inhibit the enzyme. AdoMac was resolved into its four pure diastereomeric forms, and each diastereomer was evaluated as an irreversible inhibitor of the enzyme. The K_I values for the individual diastereomers range between 3.83 and 39.6 μM, with the cis-1S,4R diastereomer being the most potent inhibitor. However, the k_inact values for the four diastereomers are not significantly different, suggesting that the binding of each diastereomer to the enzyme is configuration-dependent, while the subsequent inactivation likely proceeds through a single intermediate which is formed from each of the four diastereomers. Since each pure diastereomer represents a distinct conformational mimic exhibiting restricted sidechain rotation, the data suggests that these and related analogues may be useful as conformational probes for the catalytic site of AdoMet-DC.     

Intramolecular carboxylate catalysis in the depurination of a 7-methylguanosine derivative

We have compared the pH-independent rates of glycosidic hydrolysis in a carboxylate-bearing 7-methylguanosine derivative with those of a reference compound and with that of 7-methylguanosine itself. A syn-oriented carboxylate group affords catalysis in the hydrolysis reaction, although the instability of 7-alkylguanosines above pH 7 severely limits the useful pH range that could be studied. The effect of the carboxylate near neutral pH can be viewed in three different ways: it provides a 3-fold acceleration as compared to underivatized 7-methylguanosine, an approximately 30-fold acceleration when the decelerating effect of the ketal group is considered, and because of slow decomposition of the reference compound under the reaction conditions, we conclude that the carboxylate provides an acceleration of ≥43-fold as compared to the protio reference compound.     

Performance of a new family of modular,bed-supported,chromatography devices

Prepacked chromatography columns and cassette filtration units offer many advantages in bioprocessing. These include reduced labor costs and processing times, ease of storage, and enhanced process flexibility. Rectangular formats are particularly attractive as they can be easily stacked and multiplexed together for continuous processing. Cylindrical chromatography beds have dominated bioprocessing even though their bed support and pressure-flow performance vary with bed dimensions. This work presents the performance of novel, rhombohedral chromatography devices with internally supported beds. They are compatible with existing chromatography workstations and can be packed with any standard commercial resin. The devices offer pressure-flow characteristics independent of container-volume, simple multiplexing, and separation performance comparable to cylindrical columns. Their bi-planar, internal bed support allows mechanically less-rigid resins to be used at up to four times higher maximal linear velocities, and productivities approaching 200 g/L/h for affinity resins, compared to the 20 g/L/h typical of many column-based devices. Three 5 L devices should allow processing of up to 3 kg of monoclonal antibody per hour.     

Proteolytic processing of the vitellogenin precursor in the boll weevil,Anthonomus grandis

The soluble proteins of the eggs of the coleopteran insect Anthonomus grandis Boheman, the cotton boll weevil, consist almost entirely of two vitellin types with M_rs of 160,000 and 47,000. We sequenced their N-terminal ends and one internal cyanogen bromide fragment of the large vitellin and compared these sequences with the deduced amino acid sequence from the vitellogenin gene. The results suggest that both the boll weevil vitellin proteins are products of the proteolytic cleavage of a single precursor protein. The smaller 47,000 M vitellin protein is derived from the N-terminal portion of the precursor adjacent to an 18 amino acid signal peptide. The cleavage site between the large and small vitellins at amino acid 362 is adjacent to a pentapeptide sequence containing two pairs of arginine residues. Comparison of the boll weevil sequences with limited known sequences from the single 180,000 M_r honey bee protein show that the honey bee vitellin N-terminal exhibits sequence homology to the N-terminal of the 47,000 M_r boll weevil vitellin. Treatment of the vitellins with an N-glycosidase results in a decrease in molecular weight of both proteins, from 47,000 to 39,000 and from 160,000 to 145,000, indicating that about 10–15% of the molecular weight of each vitellin consists of N-linked carbohydrate. The molecular weight of the deglycosylated large vitellin is smaller than that predicted from the gene sequence, indicating possible further proteolytic processing at the C-terminal of that protein. © 1993 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

1,25-dihydroxyvitamin D3 and macrophage colony-stimulating factor-1 synergistically phosphorylate talin

Macrophage colony stimulating factor (CSF-1) and 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) are potent inducers of macrophage differentiation. Both appear to modulate protein phosphorylation, at least in part, through protein kinase C (PKC) raising the question as to whether they concurrently impact on macrophage-like cells. In this regard, we utilized the CSF-1 dependent murine macrophage-like line BAC 1.25F5. CSF-1 treatment of these cells for 30 min leads to particular phosphorylation of a 165 kDa protein, the putative CSF-1 receptor, and a 210 kDa moiety. 1,25(OH)₂D₃ exposure for 24 h prior to addition of CSF-1 enhances phosphorylation of the 165 kDa species and, especially, the 210 kDa protein. Phosphorylation of the latter protein is 1,25(OH)₂D₃ dose- and time-dependent and the molecule is specifically immunoprecipitated with a rabbit polyclonal anti-talin antibody. Experiments with okadaic acid show that the enhanced phosphorylation of talin does not result from serine phosphatase inhibition. CSF-1 and 1,25(OH)₂D₃, alone or in combination, do not increase talin protein expression. The tyrosine kinase inhibitor, genestein, blocks 1,25(OH)₂D₃/CSF-1 induced phosphorylation of the putative CSF-1 receptor but has no effect on talin phosphorylation which occurs exclusively on serine. In contrast to genestein, staurosporin, an inhibitor of PKC, inhibits phosphorylation of talin. Moreover, exposure of 1,25(OH)₂D₃ pretreated cells to phorbol 12-myristate 13-acetate (PMA) in place of CSF-1 also prompts talin phosphorylation. Finally, 1,25(OH)₂D₃ enhances ³[H]PDBu binding, indicating that the steroid increases PMA receptor capacity. Thus, CSF-1 and 1,25(OH)₂D₃ act synergistically via PKC to phosphorylate talin, a cytoskeletal-associated protein.