Rapid purification and molecular modeling of AaIT peptides from venom of Androctonus australis

As recombinant viruses expressing scorpion toxins are moving closer toward the market, it is important to obtain large amounts of pure toxin for biochemical characterization and the evaluation of biological activity in nontarget organisms. In the past, we purified a large amount of Androctonus australis anti-insect toxin (AaIT) present in the venom of A. australis with an analytical reversed-phase column by repeated runs of crude sample. We now report 20 times improved efficiency and speed of the purification by employing a preparative reversed-phase column. In just two consecutive HPLC steps, almost 1 mg of AaIT was obtained from 70 mg crude venom. Furthermore, additional AaIT was obtained from side fractions in a second HPLC run. Recently discovered insect selective toxin, AaIT5, was isolated simultaneously from the same venom batch. It shows different biological toxicity symptoms than the known excitatory and depressant insect toxins. AaIT5 gave 100% mortality with a dose of less than 1.3 μg against fourth-instar tobacco budworms Heliothis virescens 24 h after injection. During the purification process, we implemented mass spectrometry in addition to bioassays to monitor the presence of AaIT and AaIT5 in the HPLC fractions. Mass spectrometric screening can unambiguously follow the purification process and can greatly facilitate and expedite the downstream purification of AaIT and AaIT5 eliminating the number of bioassays required. Further, electrospray ionization was compared with matrix-assisted desorption/ionization and evaluated as a method of choice for mass spectrometric characterization of fractions from the venom purification for it provided higher mass accuracy and relative quantitation capability. Molecular models were built for AaIT5, excitatory toxin AaIT4, and depressant toxin LqhIT2. Three-dimensional structure of AaIT5 was compared with structures of the other two toxins, suggesting that AaIT5 is similar to depressant toxins. Arch. Insect Biochem. Physiol. 38:53–65, 1998. © 1998 Wiley-Liss, Inc.     

Psychometric curves of lateral facilitation

Visibility of an oriented stimulus may be enhanced by nearby stimuli that are co-aligned with the target. However, the underlying mechanism governing this facilitation is controversial. Here we measured the dependence of percent correct detection on the target's contrast (psychometric curve) with and without flankers, where flankers were either collinear with or orthogonal to the target. We find that the effect of collinear flankers can be described as a translation of the psychometric function along the linear contrast axis. This behavior is consistent, within experimental error, with two types of models: (1) non-linear transduction of target contrast with collinear flankers having additive effects on contrast, and (2) uncertainty reduction (Pelli, 1985) by collinear flankers. We discuss properties of collinear facilitation that can help deciding between these two models.     

Effects of denaturation and methylation on the degradation of proteins in cultured hepatoma cells and in reticulocyte cell-free systems

Radioiodinated, native and denatured bovine serum albumin (albumin) beta-lactoglobulin and cytochrome c were introduced into hepatoma tissue culture cells by erythrocyte-ghost-mediated microinjection, and their rates of degradation were compared. Denatured albumin was degraded at 20% of the rate of undenatured albumin, denatured beta-lactoglobulin was degraded three times faster than undenatured beta-lactoglobulin, while denatured and undenatured cytochrome c were degraded at the same rate. Thus, denaturation does not affect the rates of intracellular breakdown of microinjected proteins in a simple predictable way. Exhaustive methylation did not inhibit the degradation of denatured beta-lactoglobulin or albumin, indicating that, like their undenatured counterparts, they are not degraded via the ubiquitin pathway. In reticulocyte lysates, in the presence of ATP, denatured albumin and beta-lactoglobulin were broken down at slightly slower rates than the parent proteins. Exhaustive methylation of both denatured and undenatured proteins completely abolished their ATP-dependent breakdown. This inhibition is consistent with the hypothesis that free -NH2 groups are required for the attachment of ubiquitin prior to degradation in this system. Removal of an ammonium sulfate fraction from reticulocyte lysates produces a proteolytic system markedly different from the whole lysate [Speiser, S. & Etlinger, J. D. (1983) Proc. Natl Acad. Sci. USA 80, 3577-3580]. In this system both denatured and undenatured albumin and beta-lactoglobulin were degraded essentially independently of ATP. Methylation only slightly decreased the breakdown of denatured proteins, suggesting that they are not degraded via the ubiquitin pathway. A possible explanation of these results is that removal of the ammonium sulfate fraction unmasks an ATP-independent proteolytic system unrelated to the ubiquitin pathway.     

Alleviation of Stress-Induced Damage to Rat Brain Cells by Transcranial Electromagnetic Stimulation

Biophysics - The effect of transcranial electromagnetic stimulation on immobilization stress-induced damage to rat brain cells was studied. Electromagnetic stimulation was performed by microwave...     

Permutation pattern discovery in biosequences.

Functionally related genes often appear in each other's neighborhood on the genome; however, the order of the genes may not be the same. These groups or clusters of genes may have an ancient evolutionary origin or may signify some other critical phenomenon and may also aid in function prediction of genes. Such gene clusters also aid toward solving the problem of local alignment of genes. Similarly, clusters of protein domains, albeit appearing in different orders in the protein sequence, suggest common functionality in spite of being nonhomologous. In the paper, we address the problem of automatically discovering clusters of entities, be they genes or domains: we formalize the abstract problem as a discovery problem called the (pi)pattern problem and give an algorithm that automatically discovers the clusters of patterns in multiple data sequences. We take a model-less approach and introduce a notation for maximal patterns that drastically reduces the number of valid cluster patterns, without any loss of information, We demonstrate the automatic pattern discovery tool on motifs on E. Coli protein sequences.     

Chromosome number and genetic system in several Trifolium species related to T. alexandrinum

Chromosome counts have been done in 12 species of Trifolium, closely related to T. alexandrinum L., and the chiasma frequency in meiosis, pollen fertility, and seedset upon selfing was estimated. In all species, the basic number of chromosomes was 2n=16 arranged in eight bivalents. Two species, T. salmoneum Mout, and T. berytheum Boiss., have 0–7 B-chromosomes in eight out of nine plants examined. The frequency of B-chromosomes was somewhat correlated with pollen fertility. Chiasma frequency ranged between 10.8 and 16.1 per cell with specific and ecotypic differentiation. Except for T. alexandrinum, the species analyzed were completely (or, in a few cases, highly) self-incompatible.Contribution from the Volcani Institute of Agricultural Research, Bet Dagan, Israel. 1970 Series, No. 1677 E. This research was financed by a grant from the U.S.D.A. under P.L. 480, Contract A10-CR-56.     

The gene encoding vasoactive intestinal peptide is located on human chromosome 6p21→6qter

Summary Vasoactive intestinal peptide (VIP) is a regulatory neuropeptide involved in a wide variety of functions, among them vasodilation, smooth muscle relaxation, sweat secretion, gastrointestinal peristalsis, and pancreatic function. A deficient VIP-innervation of sweat glands was recently described as a possible pathogenic factor in sweating of cystic fibrosis (CF) patients. To investigate a possible role for a defective VIP-gene in cystic fibrosis, we have used a panel of rodent-human hybrid cells, retaining defined complements of human chromosomes to localize the VIP-gene to the human chromosome region 6p216qter. As the CF gene was recently mapped to chromosome 7, we conclude that the VIP-gene is not the primary gene defect in this disease.     

Phosphorus in the soil-plant-animal ecosystem

Summary A compartmental model of phosphorus in soil-plant-animal ecosystem is described. It consists of 17 compartments, five in soil, six in plant, three in above ground fauna and three in soil organisms and microorganisms. Common amounts and rates of turnover in each of these compartments is presented. Though the total amount of P in the ecosystem is large, only a very small part of it is being cycled, and presented data show that removal of P from an agricultural pastoral ecosystem is very slight. Most of the available phosphorus which is absorbed by plant roots is gradually fixed in forms of long-range unavailability, both by plants and by animals. This process of biological fixation is counterbalanced mainly by the activity of soil microorganisms. Quantities of input-output of P in intensive pastoral ecosystems are also presented, and some agronomical and ecological implications are considered. The manipulation of soil microorganisms and change towards more desirable P releasing strains or species may decrease need of fertilization, lower the risk of eutrophication and enhance productivity of such ecosystems. Such manipulations, however, can be achieved only after appropriate research.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. 1976 Series No. 160-EThis paper was presented as a lecture at the first N.H. Tadmor Memorial Meeting, December 1974, Jerusalem, Israel