GLUCOSE AND PYRUVATE CATABOLISM IN LITOMOSOIDES-CARINII

The filarial worm L. carinii showed a rapid uptake of glucose during in vitro incubation. This uptake proceeded linearly with time, and was significantly higher under aerobic compared to anoxic conditions. Under an atmosphere of N the worms converted glucose almost quantitatively to lactate; in the presence of O2 appreciable quantities of acetate, acetoin and CO2, in addition to lactate, were formed. Although aerobically only 73% of the carbohydrate C could be accounted for by the latter products as well as by a net glycogen synthesis, attempts to identify other compounds presumed to be derived from glucose metabolism were unsuccessful. The complete sequence of the glycolytic enzymes was detected in particulate-free cytosolic extracts of the filarial worm. With the exception of 6-phosphofructokinase, all glycolytic enzyme activities were considerably higher than those reported for rat liver. L. carinii possesses the entire set of enzymes catalyzing the 8 successive reaction steps of the tricarboxylic acid cycle. On a mitochondrial protein basis, the specific activities of these enzymes were similar to those present in rat liver. Various enzymatic activities of the mitochondrial respiratory chain were detected in the parasite. These include low levels of NADH and cytochrome c oxidases, but a high activity value for NADH dehydrogenase. Cell-free extracts and the mitochondrial fraction of the worms exhibited an enzyme capable of catalyzing the decarboxylation of pyruvate. Since this activity was stimulated 5- to 20-fold by the cofactors known to be required by the pyruvate dehydrogenase complex of other animal cells, pyruvate decarboxylation and thus acetate formation in the parasite may be mediated by an enzyme similar to, or identical with, the pyruvate dehydrogenase system. Isotopic C balance studies and experiments in which substrates specifically labeled with 14C were employed showed that substrate C can to some extent enter into respiratory CO2. Complete oxidation of C substrate may be of relevance as an energy-conserving pathway in the filarial worm.