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Ubiquinone. Biosynthesis of quinone ring and its isoprenoid side chain. Intracellular localization

100%

Szkopinska A.

nr 2

Ubiquinone, known as coenzyme Q, was shown to be the part of the metabolic pathways by Crane et al. in 1957. Its function as a component of the mitochondrial respiratory chain is well established. However, ubiquinone has recently attracted increasing attention with regard to its function, in the reduced form, as an antioxidant. In ubiquinone synthesis the para-hydroxybenzoate ring (which is the derivative of tyrosine or phenylalanine) is condensed with a hydrophobic polyisoprenoid side chain, whose length varies from 6 to 10 isoprene units depending on the organism. para-Hydroxybenzoate (PHB) polyprenyltransferase that catalyzes the condensation of PHB with polyprenyl diphosphate has a broad substrate specificity. Most of the genes encoding (all-E)-prenyltransferases which synthesize polyisoprenoid chains, have been cloned. Their structure is either homo- or heterodimeric. Genes that encode prenyltransferases catalysing the transfer of the isoprenoid chain to para-hydroxybenzoate were also cloned in bacteria and yeast. To form ubiquinone, prenylated PHB undergoes several modifications such as hydroxylations, O-methylations, methylations and decarboxylation. In eukaryotes ubiquinones were found in the inner mitochondrial membrane and in other membranes such as the endoplasmic reticulum, Golgi vesicles, lysosomes and peroxisomes. Still, the subcellular site of their biosynthesis remains unclear. Considering the diversity of functions of ubiquinones, and their multistep biosynthesis, identification of factors regulating their cellular level remains an elusive task.

The respiratory chain of rat liver mitochondria as a probe for toxicological tests in water

100%

Bragadin M. , Manente S. , Jero A. , Perin G.

nr 3

The respiratory rate of the mitochondrial respiratory chain is very sensitive to many toxins; some toxins enhance, while others slow the respiratory rate. We propose, therefore, a new simple "in vitro" method in order to assess acute toxicity in water using the response of the mitochondrial respiratory chain from rat liver. On the basis of the response we subdivided all tested toxins into two categories and for each toxin the EC50I value (which is the dose of toxin necessary to halve the maximal respiratory rate) and the EC50u value (which is the uncoupler dose necessary to stimulate the respiratory rate up to fifty percent of its maximum value) are calculated. The comparison between EC50 and LC50 values obtained by fish method allowed us to conclude that our method is a good tool for predicting the toxicity response in fish.

Inhibition of A.castellanii uncoupling protein activity by GTP depends on the redox state of quinone

67%

Swida A. , Czarna M. , Antos N. , Raczynska M. , Jarmuszkiewicz W.

nr 2 Spec.Vol.