Proline in Fascioliasis: I. Comparative Activities of Ornithine-d-Transaminase and Proline Oxidase in Fasciola and in Mammalian Livers

Abstract

The source was sought for the high levels of proline observed in the bile of animals infected with Fasciola hepatica. Toward this end the activities of 2 key enzymes in the metabolism of proline were measured. Ornithine-4-transaminase was compared in homogenates of Fasciola, rabbit liver, and rat liver. The specific activity of the Fasciola enzyme is more than 10 times greater than that of rabbit liver and more than 7 times greater than that of rat liver. Furthermore, proline oxidase which breaks down proline in mammalian liver was absent or very low in homogenates of Fasciola. These observations strongly suggest that the worm is the source of the excessive free proline. Recent studies by Kurelec and Rijavec (1966) and Isseroff et al. (1972) have shown that free proline makes up 25 to 30% of the total free amino acid nitrogen in the trematode, Fasciola hepatica. In the latter study an increase in the total free amino acid concentration was observed in the bile of infected animals. While most free amino acids increased by approximately 40 times normal concentration, proline exhibited the greatest change in concentration with increases up to 10,000-fold. Because an increase of this magnitude in a single amino acid was likely to be of significance in the host-parasite relationship, it was of interest to determine the origin of the excessive proline. From data in the study cited above (Isseroff et al., ibid.) it was known that the concentration of proline in the worm itself was always greater than in the bile, while analysis of host tissues revealed proline in concentrations as low as those in uninfected controls. Yet it was not likely that the worms were concentrating proline from the bile. Studies by Isseroff and Read (1969) had shown that proline uptake by the worm in 2min incubations is a linear function of increasing concentration, indicating uptake by simple diffusion. Furthermore, Moss (1970) observed that proline was one of the major free amino acids excreted by Fasciola in in-vitro