Inhibitory effect of a-amanitin on the induction of delta-aminolevulinate synthetase in chick embryo liver

Amatoxins, phallotoxins, phallolysin, and antamanide: the biologically active components of poisonous Amanita mushrooms

This review gives a comprehensive account of the molecular toxicology of the bicyclic peptides obtained from the poisonous mushrooms of the genus Amanita. The discussion of the biochemical events will be preceded by a consideration of the chemistry of the toxic peptides. The structural features essential for biological activities of both the amatoxins and the phallotoxins will be discussed, also including the most important analytical data. Similar consideration will be given to antamanide, a cyclic peptide, which counteracts phalloidin. In addition, the phallolysins, three cytolytic proteins from Amanita phalloides will be discussed. The report on the biological activity of the amatoxins will deal with the sensitivity of the different RNA-polymerases towards the toxins and with their action on various cell types. Consideration will also be given to systems in which alpha-amanitin was used and can be used as a molecular tool; in the past, many investigators used the inhibitor in molecular biology, genetics, and even in physiological research. As for the phallotoxins, discussion of the affinity of these toxins for actin is provied. Further discussion attempts to understand the course of intoxication by filling in the gap between the first molecular event, formation of microfilaments, and the various lesions in hepatocytes during the intoxication.

The regulation of haemoglobin synthesis in cultured chick blastoderms by steroids related to 5beta-androstane

1. After 24h of incubation, the blastoderm may be dissected from the early developing chick embryo and successfully maintained under conditions of organ culture in vitro. 2. Low concentrations of steroids related to 5beta-androstane stimulate the synthesis of foetal haemoglobins, types E and P, in a highly steroid- and tissue-specific manner.

Enhancement of RNA synthesis in avian liver cell cultures by a 5beta-steroid metabolite during induction of delta-aminolevulinate synthase

The porphyrin-heme pathway is controlled in the liver at the level of the mitochondrial enzyme delta-aminolevulinate synthase (EC 2.3.1.37), a protein inducible in cultured avian hepatocytes by a variety of chemicals including certain 5beta-metabolites of steroid hormones. The great sensitivity of the induction process to inhibition by agents known to block transcriptional activity of genetic material suggests that some control mechanism may be operating at this level to regulate the formation of the enzyme. We report here enhancement of nuclear RNA synthesis and of Mn(2+)-(NH(4))(2)SO(4)-stimulated DNA-dependent RNA polymerase (EC 2.7.7.6) activities by the 5beta-steroid metabolite, 3alpha-hydroxy-5beta-androstan-17-one (etiocholanolone), in cultured avian hepatocytes during induction of the enzyme. These changes were demonstrated in the G(1) phase of the hepatocyte cell cycle at a time when DNA synthesis is constant. Our findings support the view that one of the early steps in the process of induction of delta-aminolevulinate synthase by steroid metabolites requires new RNA synthesis, very probably messenger RNA, suggesting a 5beta-steroid transcriptional control mechanism for induction of this protein.

Rapid enhancement of chick intestinal DNA-dependent RNA polymerase II activity by 1 alpha, 25-dihydroxyvitamin D3, in vivo

1alpha,25-dihydroxyvitamin D(3) was examined for its ability to affect the DNA-dependent RNA polymerases (nucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6) of rachitic chick intestinal cell nuclei in vivo. Nucleoplasmic (form II) RNA polymerase activity was stimulated 2-fold (P < 0.05) within 2-3 hr after an oral dose of 0.27 mug (0.65 nmol) of 1alpha,25-dihydroxyvitamin D(3) to rachitic chicks. The form II polymerase activity returned to control values by 5-9 hr after dosing with the sterol. In contrast, the nucleolar (form I) RNA polymerase was not increased within this period. Solubilization of nuclear protein and resolution of the two RNA polymerases on DEAE-Sephadex also revealed that there was an increase in polymerase II activity when assayed on exogenous DNA template. This evidence suggests that 1alpha,25-dihydroxyvitamin D(3) acts at the level of the enzymology of intestinal cell transcription and that increased mRNA synthesis after administration of this hormone cannot be due solely to a change in chromatin template activity.