The biochemistry of cestode mitochondria, i. aerobic metabolism of mitochoindria from Taenia taeniaeformis

Abstract

1. 1. The oxidative capacity of mitochondrial fractions isolated from larval and adult Taenia taeniaeformis was assayed polarographically in the presence of various substrates and inhibitors. α-Glycerophosphate was the substrate most readily oxidized. Malate and NADH were oxidized at substantially lower rates; other tricarboxylic acid cycle intermediates, amino-acids, and fatty acids were either less effective or inert as substrates. 2. 2. Dihydroxyacetone phosphate was the product of α-glycerophosphate oxidation. Hydrogen peroxide was not detected, but the presence of an active catalasc may have prevented its identification. 3. 3. α-Glycerophosphate oxidation in the mitochondrial fractions was not mediated by pyridine nucleotide, but was stimulated by vitamin Kj. The cytoplasm of the parasite contained an extramitochondrial α-glycerophosphate dehydrogenase that catalysed the oxidation of NADH in the presence of dihydroxyacetone phosphate. This pair of enzymes provides the essential components of the a-glycerophosphate cycle. 4. 4. The activity of the mitochondrial a-glycerophosphate oxidase was inhibited by dicoumarol. Antimycin and cyanide were less effective, and there was little definitive evidence of a classic cytochrome system participating in the terminal electron transport. 5. 5. Oxidation of a-glycerophosphate was inhibited by several metal-chelating agents. These observations, together with the finding of substantial amounts of non-haem relative to haem iron in the mitochondrial preparations, suggest that non-haem iron has a functional role in the tapeworm respiratory chain. 6. 6. Both oxidized and reduced pyridine nucleotide were found in these preparations, and inhibition of malate oxidation was demonstrated with rotenone or Amytal (amylobarbitone). 7. 7. The respiratory chain of T. taeniaeformis appears to contain the following components: flavoprotein dehydrogenases, non-haem iron, pyridine nucleotide, and a branched cytochrome system, one portion sensitive to cyanide and the other insensitive. 8. 8. The presence of high endogenous ATPase activity in the mitochondrial fractions may indicate that the organelles were functionally altered during isolation with respect to the coupled phosphorylation reactions, which were not demonstrable.