The molecular form of mercury in biota: identification of novel mercury peptide complexes in plants.

The molecular structure of a variety of novel mercury-phytochelatin complexes was evidenced in rice plants exposed to inorganic mercury (Hg2+) using RP-HPLC with simultaneous detection via ICP-MS and ES-MS.

Ecdysone 20-monooxygenase: characterization of an insect cytochrome p-450 dependent steroid hydroxylase.

Ecdysone 20-monooxygenase, the enzyme system that hydroxylates ecdysone at C-20 of the side-chain to form ecdysterone, has been characterized in the fat body of early last instar larvae of the tobacco hornworm, Manduca sexta, using a radioenzymological assay. Ecdysterone was demonstrated to be the product of the enzyme system by high-pressure liquid chromatography, gas-liquid chromatography and mass spectrometry. Differential centrifugation, sucrose-gradient centrifugation, electron microscopy and organelle-marker enzyme analysis revealed that ecdysone 20-monooxygenase activity is associated with the mitochondria. The enzymatic properties of ecdysone 20-monooxygenase are that it is most active in a 0.05 M phosphate buffer, is inhibited by Mg2+ and exhibits pH and temperature optima at 7.5 and 30 degrees C, respectively. The enzyme complex has an apparent Km for ecdysone of 1.60 x 10(-7) M and is competitively inhibited by its product, ecdysterone, with an apparent Ki of 2.72 x 10(-5) M. The cytochrome P-450 nature of this insect steroid hydroxylase was initially suggested by its obligate requirement for NADPH and its inhibition by carbon monoxide, p-chloromercuribenzoate, metyrapone and p-aminoglutethimide but not by cyanide. Difference spectroscopy revealed the presence of cytochrome P-450 in the fat-body mitochondrial fraction. A photochemical action spectrum of ecdysone 20-monooxygenase activity confirmed the involvement of cytochrome P-450 in this monooxygenase system.

Effect of captopril and thiorphan on the proliferation of human neoplastic cell lines and their influence on cytostatic activity of interferon alpha or cytotoxic activity of doxorubicin.

We have assessed the effect of thiorphan or captopril on proliferation of two human tumor cell lines, A549 and HL60 including their influence on the cytostatic activity of interferon alpha or doxorubicin. The results showed that captopril inhibits the proliferation of both A549 and HL60 cells lines but thiorphan has antiproliferative effect only on A549 cells in a dose-dependent manner. However, neither captopril nor thiorphan administered in combination with interferon alpha or doxorubicin enhanced cytotoxic potential of doxorubicin and cytostatic activity of interferon alpha.

Site of synthesis and phylogenetic distribution of a hemolymph trophic factor of the tobacco hornworm, Manduca sexta.

Identification of fifth instar larval Manduca sexta fat body and epidermis as sites of synthesis of a hemolymph protein (hemolymph trophic factor or HTF) was achieved using in vitro 3H-leucine incorporation into protein and subsequent immunoprecipitation of tissue homogenates. Fat body is the primary site of HTF synthesis with a maximal rate on Day 1; epidermis is a secondary site with peak synthesis on Day 0. In vitro radiolabelling followed by TCA precipitation of general protein of fat body and epidermal homogenates suggest that fat body actively elaborates protein on Days 0-5 with peak rates on Days 1 and 4, while epidermis is active on Days 0-5 with a peak rate on Day 3. Based on Anti-HTF ELISA estimates, HTF [500 to 1000 micrograms/ml] was found in the hemolymph of representatives of the insect orders Blattodea, Hemiptera, Orthoptera, and Lepidoptera and in the class Crustacea, but not in the class Merostomata. These studies suggest a possible fundamental role for HTF among modern arthropods in cuticular deposition involving both epidermis and fat body. The physiological role of HTF is undetermined.

Bidirectional modulation of mouse natural killer cell and macrophage cytotoxic activities by enkephalins.

Stimulation of a cellular immune function as measured by splenic natural killer (NK) cell activity has been described following systemic treatment with enkephalins. In this study, we evaluated the effects of the central administration of enkephalins on the splenic NK cell activity and macrophage cytotoxicity. Intracerebroventricular injection of leucine-enkephalin (LE) or methionine-enkephalin (ME) induced bidirectional modulation of NK cell and macrophage cytotoxic activities (suppression followed by enhancement). Administration of ME or LE at doses of 100 or 10 micrograms/mouse caused inhibition of NK cell and macrophage activity 2 h after injection. Enhancement of NK cells activity was observed at 96 h and macrophages cytotoxicity at 24 h after icv injection with both enkephalins. Pretreatment with naloxone (20 micrograms/mouse) inhibited the enkephalins-induced augmentation of NK cell and macrophage cytotoxic activity. These findings demonstrate that central actions of enkephalins produce changes in cytotoxicity of NK cells and macrophages.