Inhibition of Tyrosine Aminotransferase by β-N-Oxalyl-l-α,β-Diaminopropionic Acid, the Lathyrus sativus Neurotoxin

Abstract: Species differences in susceptibility are a unique feature associated with the neurotoxicity of β-N-oxalyl-l -α,β-diaminopropionic acid (l -ODAP), the Lathyrus sativus neurotoxin, and the excitotoxic mechanism proposed for its mechanism of toxicity does not account for this feature. The present study examines whether neurotoxicity of l -ODAP is the result of an interference in the metabolism of any amino acid and if it could form the basis to explain the species differences in susceptibility. Thus, Wistar rats and BALB/c (white) mice, which are normally resistant to l -ODAP, became susceptible to it following pretreatment with tyrosine (or phenylalanine), exhibiting typical neurotoxic symptoms. C57BL/6J (black) mice were, however, normally susceptible to l -ODAP without any pretreatment with tyrosine. Among the various enzymes associated with tyrosine metabolism examined, the activity of only tyrosine aminotransferase (TAT) was inhibited specifically by l -ODAP. The inhibition was noncompetitive with respect to tyrosine (K_i = 2.0 ± 0.1 mM) and uncompetitive with respect to α-ketoglutarate (K_i = 8.4 ± 1.5 mM). The inhibition of TAT was also reflected in a marked decrease in the rate of oxidation of tyrosine by liver slices, an increase in tyrosine levels of liver, and also a twofold increase in the dopa and dopamine contents of brain in l -ODAP-injected black mice. The dopa and dopamine contents in the brain of only l -ODAP-injected white mice did not show any change, whereas levels of these compounds were much higher in tyrosine-pretreated animals. Also, the radioactivity associated with tyrosine, dopa, and dopamine arising from [¹⁴C]tyrosine was twofold higher in both liver and brain of l -ODAP-treated black mice. Thus, a transient increase in tyrosine levels following the inhibition of hepatic TAT by l -ODAP and its increased availability for the enhanced synthesis of dopa and dopamine and other likely metabolites (toxic?) resulting therefrom could be the mechanism of neurotoxicity and may even underlie the species differences in susceptibility to this neurotoxin.     

Ferulic acid uptake by soybean root in nutrient culture

Ferulic acid uptake by soybean root in nutrient culture was investigated by the depletion method at different concentrations, temperatures and pH. Results showed that soybean roots absorbed this compound at greater rates in the concentrations between 0.05-mM and 1.0-mM and it was concentration dependent. Ferulic acid uptake was unaffected at pH 4.5 or 6.0 but reduced at pH 7.0. At pH 6.0, uptake rates decreased significantly with increasing temperature of nutrient solution.     

Strategies for signal amplification in nucleic acid detection

Many aspects of molecular genetics necessitate the detection of nucleic acid sequences. Current approaches involving target amplification (in situ PCR, Primed in situ Labeling, Self-Sustained Sequence Replication, Strand Displacement Amplification), probe amplification (Ligase Chain Reaction, Padlock Probes, Rolling Circle Amplification) and signal amplification (Tyramide Signal Amplification, Branched DNA Amplification) are summarized in the present review, together with their advantages and limitations.     

Allatotropic and nervous control of corpora allata in the adult male loreyi leafworm, Mythimna loreyi (Lepidoptera: Noctuidae)

Allatotropic activity is found in methanolic extracts of the brain–suboesophageal ganglion (SOG)–corpora cardiaca (CC) complex from virgin males of Mythimna loreyi Duponchel (Lepidoptera, Noctuidae). Corpora allata (CA) from 6‐day‐old virgin males exhibit low rates of release of Juvenile Hormone (JH) acid (JHA) in vitro. Release of JHA can be activated by the addition of an extract of brain–SOG–CC complex in a dose‐dependent manner, and this allatotropic activation can be sustained consistently in the continuous presence of such extracts. Based on its trypsin sensitivity and heat stability, the allatotropic factor is most likely a peptide. The allatotropic activity is dependent on the concentration of calcium ions in the medium, with the highest activation achieved beyond 2 m m . The results of nerve transection experiments suggest that both nervi corporis allati I (NCA I) and NCA II are involved in mediating the allatotropic control of CA in vitro. Isolated CA alone show significantly higher rates of release of JHA than the intact brain–SOG–CC–CA complex during the first 3 h of incubation, but the release of JHA reaches almost the same range in both groups by the end of the fourth hour of incubation.     

Insights into the toxicity mechanism of and cell response to the herbicide 2,4-D in plants

Although structurally similar to the natural plant hormone indol-3- acetic acid, auxin herbicides were developed for purposes other than growth, and have been successfully used in agriculture for the last 60 years. Concerted efforts are being made to understand and decipher the precise mechanism of action of IAA and synthetic auxins. Innumerable results need to be interconnected to resolve the puzzle of auxin biology and action mode of auxin herbicides. To date, different breakthroughs are providing more insights into the process of plant-herbicide interactions. Here we highlight some of the latest findings on how the 2,4-dichlorophenoxyacetic acid damages susceptible broadleaf plants, emphasizing the role of ROS as a downstream component of the auxin signal transduction under herbicide treatment.     

Inhibition of swarming motility of Pseudomonas aeruginosa by branched-chain fatty acids.

Pseudomonas aeruginosa is capable of moving by swimming, swarming, and twitching motilities. In this study, we investigated the effects of fatty acids on Pseudomonas aeruginosa PAO1 motilities. A branched-chain fatty acid (BCFA)--12-methyltetradecanoic acid (anteiso-C15:0)--has slightly repressed flagella-driven swimming motility and completely inhibited a more complex type of surface motility, i.e. swarming, at a concentration of 10 microg mL(-1). In contrast, anteiso-C15:0 exhibited no effect on pili-mediated twitching motility. Other BCFAs and unsaturated fatty acids tested in this study showed similar inhibitory effects on swarming motility, although the level of inhibition differed between these fatty acids. These fatty acids caused no significant growth inhibition in liquid cultures. Straight-chain saturated fatty acids such as palmitic acid were less effective in swarming inhibition. The wetness of the PAO1 colony was significantly reduced by the addition of anteiso-C15:0; however, the production of rhamnolipids as a surface-active agent was not affected by the fatty acid. In addition to motility repression, anteiso-C15:0 caused 31% repression of biofilm formation by PAO1, suggesting that BCFA could affect the multiple cellular activities of Pseudomonas aeruginosa.     

Allogibberic acid: An inhibitor of flowering in Lemna perpusilla

Allogibberic acid (I) has been identified as the compound responsible for the inhibition of flowering, increase in frond multiplication rate and decrease in frond size produced in Lemna perpusilla 6746 by autoclaved, unbuffered aqueous solutions of gibberellic acid (VII). 13-Deoxyallogibberic acid (IV), a product of autoclaving aq. GA₇ (VIII) solutions, also inhibits flowering in L. perpusilla and is about 10 times more active than allogibberic acid.     

Cellular organization in the synganglion of the mite Macrocheles muscaedomesticae (Acarina: Macrochelidae)

Summary A large DNA containing body is found in oocytes of the house cricket, Acheta domesticus. Little or no RNA synthesis is associated with the DNA body during the leptotene, zygotene, and pachytene stages of meiotic prophase I. During the early diplotene stage of development, large masses of nucleolar material begin to accumulate at the periphery of the DNA body. The onset of RNA synthesis correlates with a change in the histochemically detectable histone proteins associated with the DNA body. In ovaries of animals injected with uridine-H³, most of the label accumulates in ribosomal RNA. Autoradiographic studies show that the cytoplasm of late diplotene stage cells accumulates uridine label to a greater extent than does the cytoplasm of early diplotene stage cells. Increased transport of nucleolar material through the nuclear envelope of late diplotene stage cells accounts for the increased cytoplasmic labeling.This investigation was supported by PHS Research Grant No. GM 16440 from the Institute of General Medical Sciences, and by Grants No. L-16 and J-1 from the Health Research and Services Foundation.The authors gratefully acknowledge the technical assistance of Mrs. Marcia Andrews and Miss Celeste Malinoski.     

Biosynthesis of mono- and sesquiterpenes in peppermint from mevalonate-2-C

The volatile oil from peppermint (Mentha piperita L.) is composed primarily of monoterpenes with less than 2% sesquiterpenes. However, radioactivity from mevalonate-2-¹⁴C is incorporated into caryophyllene and other sesquiterpene hydrocarbons much more extensively than into monoterpenes by peppermint cuttings. Both mono- and sesquiterpenes show maximum incorporation of label after 6 hr (0·03% vs. 0·33% of the physiological isomer) and lose 75% of the incorporated label after an additional 6 hr. Caryophyllene derived from mevalonate-2-¹⁴C after 6 hr of incorporation was chemically degraded. The isoprenoid origin of caryophyllene was confirmed, and preferential labelling of the isopentenyl pyrophosphate derived portions of the molecule was noted. On the basis of such evidence it appears that separate sites may exist for the biosynthesis of mono- and sesquiterpenes and that an endogenous dimethylallyl pyrophosphate pool may participate in the biosynthesis of sesquiterpenes in peppermint.