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PubMed1993

Strongyloides ratti: fumarate reductase and succinate dehydrogenase activities of infective larvae.

Submitochondrial particles prepared from axenised infective (L3) larvae of S. ratti (homogonic-strain) were assayed spectrophotometrically for fumarate reductase (FR) and succinate dehydrogenase (SDH) and their kinetic properties characterised. The S. ratti FR (pH 8.2; 37 degrees C) exhibited a maximum specific activity of 3.45 nmol (min)-1 (mg protein)-1 at a sodium fumarate concentration of 0.3 mM. Interestingly, the FR activity declined at fumarate concentrations greater than 0.3 mM. The mechanism of this unusual inhibitory effect requires further study. The S. ratti SDH (pH 8.2; 37 degrees C) showed a Vmax of 17.4 nmol (min)-1 (mg protein)-1; the Kmsucc was 0.5 mM. Although the SDH:FR ratio cannot predicate vectorial electron flow as would occur in vivo, an in vitro ratio of 5.04:1 was observed for SMPs derived from S. ratti L3 larvae.

Animals↗
PubMed1995

The effect of electron transport (ET) inhibitors and thiabendazole on the fumarate reductase (FR) and succinate dehydrogenase (SDH) of Strongyloides ratti infective (L3) larvae.

The fumarate reductase (FR) and succinate dehydrogenase (SDH) activities of isolated submitochondrial particles (SMPs) prepared from axenised L3 larvae of S. ratti were characterised with respect to their response to a selected range of inhibitors. Rotenone (a specific inhibitor of electron transport Complex I) inhibited the S. ratti FR (EC50 = 3.0 x 10(-7) M) but not SDH. This strongly suggests that the S. ratti FR is functionally linked with the S. ratti ET-Complex I. 2-Thenoyltrifluoroacetone (TTFA, an inhibitor of ET-Complex II) inhibited FR (EC50 = 2.6 x 10(-5) M) and SDH (EC50 = 2.8 x 10(-5) M) with similar effectiveness. Sodium malonate (substrate analogue of succinate) had a greater affinity for SDH (EC50 = 6.8 x 10(-4) M), than FR (EC50 = 1.9 x 10(-2) M). Sodium fumarate was ca. 8-fold more effective in inhibiting the S. ratti FR (EC50 = 6.0 x 10(-4) M) than SDH (EC50 = 4.8 x 10(-3) M). The S. ratti FR was more sensitive to inhibition by thiabendazole (TBZ; EC50 = 4.6 x 10(-4) M) than SDH (EC50 > 1.0 x 10(-3) M), suggesting that one of the sites-of-action of TBZ to be the FR of S. ratti mitochondria. More potent inhibitors of S. ratti FR, if developed, may prove to be effective chemotherapeutic agents in the management of human strongloidiasis.

Animals↗
PubMed1995

Strongyloides ratti: mitochondrial enzyme activities of the classical electron transport pathway in the infective (L3) larvae.

Submitochondrial particles prepared from S. ratti L3 larvae exhibited NADH-oxidase (NOX), NADH-ferricyanide reductase (NFR), NADH-cytochrome-c-reductase (NCR), succinate-cytochrome-c-reductase (SCR), and cytochrome-aa3-oxidase activities of 2.1 +/- 0.3, 8.9 +/- 1.3, 0.6 +/- 0.1., 1.0 +/- 0.2 and 1.2 +/- 0.3 nm min-1 mg protein-1 respectively, at 37 degrees C. The NCR and NOX activities were 39.3% and 23.5% of the NFR activity, suggesting the occurrence of a rate-limiting step or bifurcation of the respiratory electron transport (RET) pathway on the oxygen-side of RET-Complex I. The NCR activity was 50% that of cytochrome-aa3-oxidase activity which suggests partitioning of electron flow at the level of RET-Complex III and/or the quinone-function. Antimycin A and rotenone but not 2-thenoyl trifluoroacetone (TTFA) inhibited NCR activity, the EC50 values were 3.6 x 10(-6) M, 3.7 x 10(-7) M, respectively. SCR activity was inhibited by antimycin A (EC50 = 3.8 x 10(-6) M) and TTFA (EC50 = 2.8 x 10(-5) M) but not by rotenone. The results suggest that presence of classical and alternate RET-pathways in S. ratti L3 larvae.

Animals↗