[H-3] AMINO-ACID-UPTAKE AND METABOLIC STUDIES ON GIGANTOCOTYLE EXPLANATUM AND GASTROTHYLAX CRUMENIFER (DIGENEA PERPENDICULAR-TO, PARAMPHISTOMIDAE)

The amphistomes Gigantocotyle explanatum and Gastrothylax crumenifer u tilize leucine, alanine, proline and methionine during in vitro incuba tions. Autoradiography on sections of these flukes reveal a time-depen dent differential incorporation of tritium-labelled amino acids in var ious tissues. The tegument appears to be the primary surface through w hich amino acids are absorbed. Following absorption, the reappearance of [H-3]-leucine and [H-3]-alanine on the tegumental surface during la te chase periods indicates their possible involvement in tegumental se cretion. A combination of diffusion and carrier-mediated uptake, possi bly involving gamma-glutamyl transpeptidase, is indicated. The transpo rt loci show differences in carrier-affinity (K-t) and maximum uptake velocities (V-max) or amino acids under study, which suggest multiple transport molecules. Metabolic studies reveal that aspartate, alanine, ornithine, proline, leucine and methionine undergo transamination thr ough 2-oxoglutarate-linked transaminases, distributed in the cytosolic and mitochondrial fractions of G. explanatum and G. crumenifer. With the exception of alanine transaminase, the enzyme levels in the cytoso lic fraction were higher than the mitochondrial fraction of the two am phistomes. Predominently cytosolic glutamate dehydrogenase which was c omparatively higher in C. explanatum,, catalyse amination of alpha-ket oglutarate. A high level of cytosolic arginase alone does not indicate a functional urea cycle. A tentative pathway of amino acid metabolism in these amphistomes is proposed.