Effect of Bt-cotton on chrysopids, ladybird beetles and their prey: aphids and whiteflies.

The effect of Bt-cotton, i.e. genetically modified cotton that contain genes expressing delta-endotoxin, on aphid, whitefly, chrysopid and coccinellid populations was determined with a two-year field study at a cotton farm near Marble Hall, South Africa. Although Bt-cotton is lepidopteran specific, non-lepidopteran arthropod populations may be indirectly influenced by the endotoxin. Abundance of aphid, whitefly, chrysopid and coccinellid populations and predator-prey interactions were used as measures to determine possible effects on the populations under investigation. The cultivation of Bt-cotton had no effect on aphid, whitefly, chrysopid or coccinellid abundance. Positive density dependent interactions occurred between aphids and coccinellids which were not influenced by Bt-cotton. A significant relationship between whitefly and coccinellid abundance, i.e. predator-prey reaction, occurred in the control and sprayed non-Bt cotton fields but was absent from the Bt-cotton fields.

Determination of the ratios of the aromatic amino acid residues by first- or second-derivative UV spectrometry for a simple characterization of peptides.

A method for the simultaneous determination of the ratios of the three aromatic amino-acid residues in peptides was set up in acidic conditions. Binary and ternary mixtures of these amino acids were prepared, and first- and second-derivative spectra then calculated from their 0.1 nm resolution spectra between 240 and 320 nm. Certain spectral bands were chosen to differentiate tyrosine from tryptophan on the first-derivative spectra, and phenylalanine from tyrosine and tryptophan on the second-derivative spectra. Variation of the amplitude of the chosen bands was shown to be a linear function of the ratio of the aromatic amino acids in the mixture. This technique was validated with peptides whose sequence was known. The difference between theoretical and experimentally determined ratios was lower than 10%. Since the results are obtained as ratios, neither the concentration nor the nature of the peptide has to be known. The feasibility of application using a photodiode array detector with high resolution in reversed-phase high-performance liquid chromatography is discussed.

Stable insulin for implantable delivery systems: in vitro studies with different containers and solvents.

The stability of a new insulin formulation (lyophilized U100 insulin, Organon) was investigated in vitro in conditions reproducing those of in vivo implanted devices, i.e., constant horizontal agitation at 37 degrees C for 4 wk in various containers and 8 wk in different solvents. Physical stability was assessed by ultraviolet absorption, chemical stability by HPLC, and biological stability by hypoglycemia tests in mice. Insulin precipitated in glass vials but remained clear and active in polyethylene reservoirs and after passage through catheter and pumps in motion, although only 83-90% of insulin was delivered chemically intact. In acidic solvent, insulin showed a major gradual transformation into deamidized derivatives (up to 78% after 8 wk), although still fully active and clear, as expected from previously published excellent in vivo results with acidic insulins. Heparin addition to neutral insulin solution (500 IU/ml) did not alter the properties of the two compounds and might thus be tried to prevent in vivo catheter obstruction due to fibrin deposition.

Pepstatin analogues as novel renin inhibitors.

Pepstatin analogues corresponding to the general formula A-X-Y-Sta-Ala-Sta-R were synthesized in solution phase. Various changes in the nature of the A, X, and Y groups were made to improve the inhibitory potency against human plasma renin activity. The results were interpreted by use of the active-site model based on the sequence of human angiotensinogen. The tert-butyloxycarbonyl group and the isovaleryl group were found to be the most effective acyl groups (A). The analogues having a Phe residue in place of Val1 (X) and His or amino acid with an aliphatic side chain such as norleucine or norvaline in the Y position showed the highest inhibition of human plasma renin activity with IC50 values of about 10(-8)M. Esterification or amidification of the carboxyl group of the C-terminal statine did not change the inhibitory potency. The selectivity for rat, dog, pig, and monkey plasma renin of the most interesting compounds was studied.

Comparison of radioimmunoassay, chemical assay (HPLC) and bioassay for arginine vasopressin in synthetic standards and posterior pituitary tissue.

Radioimmunoassay and chemical assay (high performance liquid chromatography (HPLC) with fluorescence detection) for arginine vasopressin (AVP) in purified synthetic preparations and in posterior lobe tissue samples (ox and rat) yielded essentially identical values. In tissue samples from the neurohypophysis, the reproducibility of the former method was roughly twice as good. The routinely used blood pressure bioassay was very poorly reproducible and yielded values deviating from the two ther methods. In all three assays, the coefficient of variation was roughly five times higher in tissue samples than in synthetic preparations. It is suggested that a chemical rather than a biological assay is used for standardization of AVP for radioimmunoassay. Large differences were found in the quality of AVP preparations potentially usable as standards and tracers (after iodination) for radioimmunoassay. All commercial preparations should therefore be checked for their AVP and impurity content by high performance liquid chromatography.