CYTOCHROME-C PEROXIDASE IN SCHISTOSOMA-MANSONI - ENZYME-KINETICS AND CELLULAR LOCATION

Antioxidant enzymes are critical in the process of cellular response a gainst reactive species of oxygen. In mammalian cells, catalase and gl utathione peroxidase (GPx) are the principal enzymes involved in remov ing H2O2. Schistosoma mansoni does not contain catalase and has been f ound to possess a cytochrome c peroxidase linked activity in its cells . Cytochrome c peroxidase (CcP) is an enzyme isolated and extensively characterized from yeast. Our interest has been to evaluate the role o f cytochrome c peroxidase as a novel antioxidant enzyme in Schistosoma mansoni, This initial study deals with basic kinetics of the parasite enzyme and its similarities with the yeast enzyme and investigates it s cellular location. Cytochrome c peroxidase and cytochrome c oxidase enzyme activities were measured in crude enzyme extracts of Schistosom a mansoni male and female adult worms. Schistosoma mansoni CcP sharks some properties with yeast cytochrome c peroxidase, The enzymatic oxid ation of ferrocytochrome c is favoured by an acidic pH. Schistosoma ma nsoni CcP has significant affinity for cytochrome c from horse heart a nd from Saccharomyces cerevisae and it is inhibited by ferricytochrome c, potassium cyanide and sodium azide. CcP is located in the mitochon dria of Schistosoma mansoni and fractionation with digitonin indicates that the parasite enzyme is located in the intermembrane space. The K -m values for hydrogen peroxide for Schistosoma mansoni CcP and glutat hione peroxidase using horse heart cytochrome c as the electron donor were found to be 31 +/- 4.4 and 8.0 +/- 1.7 mu M respectively. Althoug h GPx has a greater affinity for H2O2 than CcP, the level of activity of CcP per mg protein is 10 times greater and is indicative of the rol e of this enzyme as a major antioxidant in Schistosoma mansoni.