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Pyruvate metabolism in castor-bean mitochondria.

ABSTRACT: We report the isolation of mitochondria from the endosperm of castor beans (Ricinus communis). These mitochondria oxidized succinate, external NADH, malate and pyruvate with respiratory-control and ADP/O ratios consistent with those found previously with mitochondria from other plant sources. The mitochondria exhibited considerable sensitivity to the electron-transport-chain inhibitors antimycin A and cyanide when oxidizing succinate and external NADH. Pyruvate-dependent O2 uptake was relatively insensitive to these inhibitors, although the residual O2 uptake could be inhibited by salicylhydroxamic acid. We conclude that a cyanide-insensitive alternative terminal oxidase is functional in these mitochondria. However, electrons from the succinate dehydrogenase or external NADH dehydrogenase seem to have no access to this pathway. There is little interconnection between the salicylhydroxamic acid-sensitive and cyanide-sensitive pathways of electron transport. alpha-Cyanocinnamate and its analogues, compound UK5099 [alpha-cyano-beta-(1-phenylindol-3-yl)acrylate] and alpha-cyano-4-hydroxycinnamate, were all found to be potent non-competitive inhibitors of pyruvate oxidation in castor-bean mitochondria. The accumulation of pyruvate by castor-bean mitochondria was determined by using a silicone-oil-centrifugation technique. The accumulation was shown to observe Michaelis-Menten kinetics, with a Km for pyruvate of 0.10 mM and a Vmax. of 0.95 nmol/min per mg of mitochondrial protein. However, the observed rates of pyruvate accumulation were insufficient to account for the pyruvate oxidation rates found in the oxygen-electrode studies. We were able to demonstrate that this is due to the immediate export of the accumulated radiolabel in the form of malate and citrate. Compound UK5099 inhibited the accumulation of [2-14C]pyruvate by castor-bean mitochondria at concentrations similar to those required to inhibit pyruvate oxidation.

SUBMITTER: Brailsford MA

PROVIDER: S-EPMC1147288 | biostudies-other | 1986 Oct

REPOSITORIES: biostudies-other

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Project description:BackgroundMicroRNAs (miRNAs) are endogenously encoded small RNAs that post-transcriptionally regulate gene expression and play essential roles in numerous developmental and physiological processes. Currently, little information on the transcriptome and tissue-specific expression of miRNAs is available in the model non-edible oilseed crop castor bean (Ricinus communis L.), one of the most important non-edible oilseed crops cultivated worldwide. Recent advances in sequencing technologies have allowed the identification of conserved and novel miRNAs in many plant species. Here, we used high-throughput sequencing technologies to identify and characterize the miRNAs in castor bean.ResultsFive small RNA libraries were constructed for deep sequencing from root tips, leaves, developing seeds (at the initial stage, seed1; and at the fast oil accumulation stage, seed2) and endosperms in castor bean. High-throughput sequencing generated a large number of sequence reads of small RNAs in this study. In total, 86 conserved miRNAs were identified, including 63 known and 23 newly identified. Sixteen miRNA isoform variants in length were found from the conserved miRNAs of castor bean. MiRNAs displayed diverse organ-specific expression levels among five libraries. Combined with criteria for miRNA annotation and a RT-PCR approach, 72 novel miRNAs and their potential precursors were annotated and 20 miRNAs newly identified were validated. In addition, new target candidates for miRNAs newly identified in this study were proposed.ConclusionsThe current study presents the first high-throughput small RNA sequencing study performed in castor bean to identify its miRNA population. It characterizes and increases the number of miRNAs and their isoforms identified in castor bean. The miRNA expression analysis provides a foundation for understanding castor bean miRNA organ-specific expression patterns. The present study offers an expanded picture of miRNAs for castor bean and other members in the family Euphorbiaceae.

Project description:BackgroundMicrosporidia is a large group of eukaryotic obligate intracellular spore-forming parasites, of which 17 species can cause microsporidiosis in humans. Most human-infecting microsporidians belong to the genera Enterocytozoon and Encephalitozoon. To date, only five microsporidian species, including Encephalitozoon-like, have been found in hard ticks (Ixodidae) using microscopic methods, but no sequence data are available for them. Furthermore, no widespread screening for microsporidian-infected ticks based on DNA analysis has been carried out to date. Thus, in this study, we applied a recently developed DNA metabarcoding method for efficient microsporidian DNA identification to assess the role of ticks as potential vectors of microsporidian species causing diseases in humans.MethodsIn total, 1070 (493 juvenile and 577 adult) unfed host-seeking Ixodes ricinus ticks collected at urban parks in the city of Poznan, Poland, and 94 engorged tick females fed on dogs and cats were screened for microsporidian DNA. Microsporidians were detected by PCR amplification and sequencing of the hypervariable V5 region of 18S rRNA gene (18S profiling) using the microsporidian-specific primer set. Tick species were identified morphologically and confirmed by amplification and sequencing of the shortened fragment of cytochrome c oxidase subunit I gene (mini-COI).ResultsAll collected ticks were unambiguously assigned to I. ricinus. Potentially zoonotic Encephalitozoon intestinalis was identified in three fed ticks (3.2%) collected from three different dogs. In eight unfed host-seeking ticks (0.8%), including three males (1.1%), two females (0.7%) and three nymphs (0.7%), the new microsporidian sequence representing a species belonging to the genus Endoreticulatus was identified.ConclusionsThe lack of zoonotic microsporidians in host-seeking ticks suggests that I. ricinus is not involved in transmission of human-infecting microsporidians. Moreover, a very low occurrence of the other microsporidian species in both fed and host-seeking ticks implies that mechanisms exist to defend ticks against infection with these parasites.

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Pyruvate metabolism in castor-bean mitochondria.

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