Vitellogenin titre in haemolymph of Locusta migratoria in normal adults,after ovariectomy,and in response to methoprene

Vitellogenin in the haemolymph of Locusta migratoria was assayed by rocket immunoelectrophoresis to elucidate aspects of its regulation. In many normal adult females, vitellogenin first appeared on days 5–9, rose quickly to peak levels, and declined before a second vitellogenic cycle; in others, it appeared later and built up more slowly. The timing of first appearance of vitellogenin, and proportions of early and late-developing individuals, differed markedly in groups from the same colony assayed in different years, suggesting effects of both genetic and environmental variation. Average peak levels of vitellogenin were 25–30 mg/ml. After ovariectomy, vitellogenin appeared near the normal time and increased for several weeks to about 300 mg/ml; haemolymph volume also increased greatly, so that the total haemolymph-vitellogenin pool reached about 300 mg/individual, or 100 times the normal amount. After ovariectomy, no cyclicity of vitellogenin accumulation was apparent. These results show that the ovary is not required for stimulation of vitellogenin synthesis, and suggest that normal cycling may depend on inhibition by the mature ovary. Females treated with ethoxyprecocene on day 1 of adult life to inactivate the corpora allata did not produce vitellogenin, but were induced to do so with the juvenile hormone analogue, methoprene. After injection of 150 μg of methoprene in mineral oil, there was one day lag, then vitellogenin increased in the haemolymph to the normal peak level and declined slowly to zero during 5 weeks; after a second injection of methoprene, vitellogenin re-appeared more rapidly, with less lag, reflecting accelerated secondary hormonal stimulation of vitellogenin synthesis in the fat body. Adult males showed no detectable haemolymph vitellogenin even after injection of large doses of methoprene.     

UPTAKE OF METHYLAMINE (AN AMMONIUM ANALOGUE) BY MACROCYSTIS PYRIFERA (PHAEOPHYTA)1

The ammonium analogue, methylamine, is taken up rapidly from dilute solution by Macrocystis pyrifera (L.) C. A. Agardh. ¹⁴C-methylamine was used to characterize the transport system, with respect to dependence on external concentration, temperature, pH and substrate specificity. The results suggest that methylamine enters the algal tissue via a specific mediated transport system. Uptake of methylamine showed no consistent relation to the N content of the plant tissue, but was highly dependent on the portion of plant sampled and severely affected by cutting the tissue. The strong inhibition of methylamine uptake by ammonium and lesser inhibition by other alkylamines suggests that the uptake system functions as an “ammonium permease”. Uptake of ¹⁴C-methylamine can be used as a highly sensitive measure of NH₄⁺ uptake activity and should be a useful tool for studying NH₄⁺ uptake in the laboratory and field.     

Inhibitory effects of anions and active site amino acid sequence of chicken liver L-2-hydroxyacid oxidase A, a member of the FMN-dependent α-hydroxyacid oxidizing enzyme family

Monocarboxylic acids with aliphatic chains were found to be mixed inhibitors of chicken liver L-2-hydroxyacid oxidase A when L-2-hydroxy-4-methylthiobutanoic acid was used as the substrate. The finding that the binding affinity of the enzyme for monocarboxylic acids was directly proportional to the number of carbon atoms in the chain strongly suggests that in addition to the electrostatic interaction due to the carboxyl moiety, hydrophobic forces may also be involved in the binding affinity of monocarboxylic acids to the enzyme's active site. Oxalate, a dicarboxylic acid, also resulted in a mixed-type inhibition of chicken liver L-2-hydroxyacid oxidase A, and, surprisingly, its binding affinity to the enzyme was found to be quite high as compared with monocarboxylic acids. This is probably due to the fact that the two carboxyl groups of oxalate give rise to electrostatic interactions with the positively charged side chains of two adjacent residues in the polypeptide chain. The inhibitory effects of other dicarboxylic acids was found to decrease as the number of carbon atoms in the chain increased. Oxamate was found however to be a novel type of potent inhibitor of the enzyme. All in all, these kinetic studies and the amino acid sequence determination in the active site region after limited proteolysis of the polypeptide chain definitely establish that chicken liver NADH/FMN containing L-2-hydroxyacid oxidase A is a member of the FMN-dependent α-hydroxyacid oxidizing enzyme family.     

Modification of [3H]MK801 Binding to Rat Brain NMDA Receptors after the Administration of a Convulsant Drug and an Adenosine Analogue: A Quantitative Autoradiographic Study

Specific [³H]MK801 binding to rat brain NMDA receptors after the administration of the convulsant drug 3-mercaptopropionic acid (MP) and the adenosine analogue cyclopentyladenosine (CPA) was studied by means of a quantitative autoradiographic method. MP administration (150 mg/kg, i.p.) caused significant decreases in [³H]MK801 binding in several hippocampus subareas and layers, mainly in CA1 and CA3 at seizure (11–27%) and postseizure (8–16%) and in cerebral occipital cortex at seizure (18–22%). In nucleus accumbens, a rise was observed at postseizure (44%) and a tendency to increase at seizure (24%). CPA (2mg/kg, i.p.) decreased ligand binding in hippocampus (CA1, CA2, CA3) (17–22%) and in occipital cerebral cortex (18–24%). When CPA was administered 30 minutes before MP (which delayed seizure onset) and rats were sacrified at seizure, decreases in [³H]MK801 binding in several layers of CA1 and CA3 of hippocampus (11–27%) and in CA1, CA2, CA3 (24–35%) after CPA+MP postseizure, and an increase in CA2 after CPA and CPA+MP postseizure (20–34%), were observed. A drop was found in the occipital subarea (18–24%) after CPA and in the frontal and occipital subarea after CPA+MP postseizure (24–34%) while no changes were observed in any treatment involving the other cerebral cortex regions, thalamic nuclei, caudate putamen and olfactory tubercle. These results show that [³H]MK801 binding changes according to drug treatment and the area being studied, thus indicating a different role in seizure activity.     

人降钙素类似物的合成及活性研究

通过对鲑鱼降钙素和人降钙素结构的比较,设计并合成了人降钙素类似物ｍｈＣＴ－２。利用空气氧化获得分子内二硫键,经分离纯化,产物达ＨＰＬＣ及毛细管电泳均一,蛋白质序列分析和质谱分析符合理论值。在大鼠降血钙生物活性测定中,利用量反应平行线法进行ｍｈＣＴ－２的生物效价判定达２０００ＩＵ／ｍｇ,比ｈＣＴ的效价高一个数量级。     

Streptomyces pulveraceus突变株中福司曲星类似物的分离鉴定及其生物合成途经初探(英文)

福司曲星是一种从Streptomyces pulveraceus分离得到的磷酸酯类、聚酮类抗生素。本文从其突变株(ΔfosJ)分离得到一系列新的福司曲星结构类似物(10～14)。结合各种波谱方法,我们对其结构进行鉴定。由于这些化合物的结构特殊性,初步推断这些化合物可能来自于异常的PKS组合生物合成。     

Ribozyme chemogenetics

In this review I will outline several chemogenetic approaches used to determine the chemical basis of large ribozyme function and structure. The term chemogenetics was first used to describe site-specific functional group modification experiments in the analysis of DNA–protein interactions. Within the past few years equivalent experiments have been performed on large catalytic RNAs using both single-site substitution and interference mapping techniques with nucleotide analogues. While functional group mutagenesis is an important aspect of a chemogenetic approach, chemical correlates to genetic revertants and suppressors must also be realized for the genetic analogy to be intellectually valid and experimentally useful. Several examples of functional group revertants and suppressors have now been obtained within the Tetrahymena group I ribozyme. These experiments define an ensemble of tertiary hydrogen bonds that have made it possible to construct a detailed model of the ribozyme catalytic core. The model includes a functionally important monovalent metal ion binding site, a wobble–wobble receptor motif for helix–helix packing interactions, and a minor groove triple helix. © 1998 John Wiley & Sons, Inc. Biopoly 48: 65–81, 1998     

Hydrophobic forces are responsible for the folding of a highly potent natriuretic peptide analogue at a membrane mimetic surface: An NMR study

A conformational study by nmr spectroscopy was performed with the highly active 28-residue hybrid natriuretic peptide analogue pBNP1 [M. Mimeault, A. De Léan, M. Lafleur, D. Bonenfant, and A. Fournier (1995) Biochemistry, Vol. 34, pp. 955–964], which consists of the cyclic peptide core of pBNP32 and the N- and C-terminal exocyclic segments of rANP(99–126). In purely aqueous solution pBNP1 exhibits random coil behavior as evidenced by the almost complete absence of structurally significant nmr observables. By contrast, elements of secondary structure emerged upon the addition of dodecylphosphocholine micelles to the aqueous sample. Nuclear Overhauser effect distance-restrained molecular dynamics simulations in conjunction with torsional angle determinations permitted the generation of a reasonable model of the lipid-bound conformation of pBNP1. According to this model, pBNP1 adopts turn-like features in the cyclic and C-terminal regions of the peptide, but remains quite flexible in the N-terminal segment. Two hydrophobic cores separated by a hydrophilic cleft were also evident in the generated structure. A mechanism is proposed whereby the hydrophobic interactions necessary to stabilize a folded structure of pBNP1 are facilitated by the presence of the membrane-like polar/apolar interface provided by the phospholipid micelles. © 1997 John Wiley & Sons, Biopoly 42: 37–48, 1997     

Synthesis and antifungal activity of two novel spermidine analogues

Two spermidine analogues were synthesised and examined for antifungal activity. Both compounds used as 1 mM post-inoculation sprays reduced infection of barley seedlings by the powdery mildew fungus, Erysiphe graminis f.sp. hordei, infection of broad bean seedlings by the rust fungus, Uromyces viciae-fabae, and infection of apple seedlings by the powdery mildew fungus, Podosphaera leucotricha. Since these fungal pathogens cannot be cultured axenically, the effects of the two spermidine analogues on mycelial growth in vitro, as well as preliminary investigations on polyamine biosynthesis, were undertaken using the oat stripe pathogen, Pyrenophora avenae. Although neither compound affected radial growth of the fungus on plates, both analogues reduced fungal biomass in liquid culture substantially. The two spermidine analogues, used at a concentration of 1 mM, had no significant effect on the conversion of labelled ornithine into polyamines in P. avenae.