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The formation of 5-phosphomevalonate by mevalonate kinase in Hevea brasiliensis latex.

ABSTRACT: 1. Evidence has been produced for the formation of 5-phosphomevalonate from potassium dl-mevalonate by the latex of Hevea brasiliensis and by reconstituted freeze-dried serum obtained from this latex. 2. The enzyme, mevalonate kinase, catalysing the formation of 5-phosphomevalonate from potassium dl-mevalonate and ATP has been partially purified. 3. 5-Phosphomevalonate formed by the purified mevalonate kinase from potassium [2-(14)C]mevalonate has been shown to be incorporated by latex into rubber to about 2.4 times the extent of dl-mevalonate. 4. The enzyme can utilize inosine triphosphate as effectively as adenosine triphosphate as a phosphate donor and is also slightly active with uridine triphosphate. 5. The enzyme was fairly stable to a range of pH values and temperatures, the activity being optimum at pH7.5 and 60-70 degrees . The energy of activation was 10.7kcal./mole. The K(m) values were 0.13mm for potassium dl-mevalonate and 2.0mm for ATP at 30 degrees . 6. The enzyme required the presence of Mn(2+) (1mm) for maximum activity; this could be replaced by Mg(2+) (4mm), which was less effective, and by Ca(2+), which was far less effective. 6. Although the enzyme did not require cysteine or reduced glutathione for activation in aerobic conditions, it was inhibited by reagents known to react with thiol groups.

SUBMITTER: Williamson IP

PROVIDER: S-EPMC1207229 | biostudies-other | 1965 Sep

REPOSITORIES: biostudies-other

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Project description:Background:Small RNAs modulate plant gene expression at both the transcriptional and post-transcriptional level, mostly through the induction of either targeted DNA methylation or transcript cleavage, respectively. Small RNA networks are involved in specific plant developmental processes, in signaling pathways triggered by various abiotic stresses and in interactions between the plant and viral and non-viral pathogens. They are also involved in silencing maintenance of transposable elements and endogenous viral elements. Alteration in small RNA production in response to various environmental stresses can affect all the above-mentioned processes. In rubber trees, changes observed in small RNA populations in response to trees affected by tapping panel dryness, in comparison to healthy ones, suggest a shift from a transcriptional to a post-transcriptional regulatory pathway. This is the first attempt to characterise small RNAs involved in post-transcriptional silencing and their target transcripts in Hevea. Methods:Genes producing microRNAs (MIR genes) and loci producing trans-activated small interfering RNA (ta-siRNA) were identified in the clone PB 260 re-sequenced genome. Degradome libraries were constructed with a pool of total RNA from six different Hevea tissues in stressed and non-stressed plants. The analysis of cleaved RNA data, associated with genomics and transcriptomics data, led to the identification of transcripts that are affected by 20-22 nt small RNA-mediated post-transcriptional regulation. A detailed analysis was carried out on gene families related to latex production and in response to growth regulators. Results:Compared to other tissues, latex cells had a higher proportion of transcript cleavage activity mediated by miRNAs and ta-siRNAs. Post-transcriptional regulation was also observed at each step of the natural rubber biosynthesis pathway. Among the genes involved in the miRNA biogenesis pathway, our analyses showed that all of them are expressed in latex. Using phylogenetic analyses, we show that both the Argonaute and Dicer-like gene families recently underwent expansion. Overall, our study underlines the fact that important biological pathways, including hormonal signalling and rubber biosynthesis, are subject to post-transcriptional silencing in laticifers.

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The formation of 5-phosphomevalonate by mevalonate kinase in Hevea brasiliensis latex.

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