Juvenile hormone synthesis: "esterify then epoxidize" or "epoxidize then esterify"? Insights from the structural characterization of juvenile hormone acid methyltransferase.

Juvenile hormones (JHs) play key roles in regulating metamorphosis and reproduction in insects. The last two steps of JH synthesis diverge depending on the insect order. In Lepidoptera, epoxidation by a P450 monooxygenase precedes esterification by a juvenile hormone acid methyltransferase (JHAMT). In Orthoptera, Dictyoptera, Coleoptera and Diptera epoxidation follows methylation. The aim of our study was to gain insight into the structural basis of JHAMT's substrate recognition as a means to understand the divergence of these pathways. Homology modeling was used to build the structure of Aedes aegypti JHAMT. The substrate binding site was identified, as well as the residues that interact with the methyl donor (S-adenosylmethionine) and the carboxylic acid of the substrate methyl acceptors, farnesoic acid (FA) and juvenile hormone acid (JHA). To gain further insight we generated the structures of Anopheles gambiae, Bombyx mori, Drosophila melanogaster and Tribolium castaneum JHAMTs. The modeling results were compared with previous experimental studies using recombinant proteins, whole insects, corpora allata or tissue extracts. The computational study helps explain the selectivity toward the (10R)-JHA isomer and the reduced activity for palmitic and lauric acids. The analysis of our results supports the hypothesis that all insect JHAMTs are able to recognize both FA and JHA as substrates. Therefore, the order of the methylation/epoxidation reactions may be primarily imposed by the epoxidase's substrate specificity. In Lepidoptera, epoxidase might have higher affinity than JHAMT for FA, so epoxidation precedes methylation, while in most other insects there is no epoxidation of FA, but esterification of FA to form MF, followed by epoxidation to JH III.

Nitrosation of melatonin by nitric oxide: a computational study.

Melatonin is being increasingly promoted as a therapeutic agent for the treatment of jet lag and insomnia, and is an efficient free radical scavenger. We have recently characterized a product for the reaction of melatonin with nitric oxide (NO), N-nitrosomelatonin. In the present work, reaction pathways with N1, C2, C4, C6 and C7 as possible targets for its reaction with NO that yield the respective nitroso derivatives have been investigated using semiempirical AM1 computational tools, both in vacuo and aqueous solution. Specifically, two different pathways were studied: a radical mechanism involving the hydrogen atom abstraction to yield a neutral radical followed by NO addition, and an ionic mechanism involving addition of nitrosonium ion to the indolic moiety. Our results show that the indolic nitrogen is the most probable site for nitrosation by the radical mechanism, whereas different targets are probable considering the ionic pathway. These results are in good agreement with previous experimental findings and provide a coherent picture for the interaction of melatonin with NO.

Isolated tricuspid valve disease in antiphospholipid syndrome.

Cardiac valve involvement in antiphospholipid syndrome (APS) has been consistently shown. However, isolated tricuspid valve disease within this syndrome has only been recently reported. We report a patient with primary antiphospholipid syndrome who had isolated tricuspid organic valve disease, pulmonary hypertension and pulmonary thromboembolism. We suggest that the APS should be listed as one of the aetiologies of organic isolated tricuspid valve disease in the adult population.

Reactions of melatonin and related indoles with free radicals: a computational study.

Melatonin is being increasingly promoted as a therapeutic agent for the treatment of jet lag and insomnia and has been recently suggested to act as an efficient free-radical scavenger. In the present work, its mechanisms of action for scavenging hydroxyl radicals have been investigated using semiempirical AM1 and density functional theory (DFT) computational tools. Two different reactions were proposed as follows: one involving the abstraction of an indolic hydrogen to yield a neutral radical and another involving the addition of the hydroxyl radical to the indolic moiety. Our results show that, from a thermodynamical standpoint, melatonin may directly scavenge hydroxyl radicals both in vacuum and in aqueous solution. The structural requirements for free-radical-trapping ability have been examined comparing melatonin with related indoles. Computational data suggest that 5-methoxy and N-acetyl groups of melatonin do not significantly affect its thermodynamical capacity of free-radical trapping. The present results support experimental data on the potential of melatonin as a physiological or pharmacological antioxidant agent.