Lipid metabolism and low molecular weight solute uptake in Ascaridia galli

Adult Ascaridia galli, an intestinal nematode parasite of fowl, reveals a large variety of complex lipids such as phospholipids containing choline, ethanolamine, inositol, serine and glycerol. Lysophospholipid species, vinyl ether phospholipid (plasmalogen), neutral acylglycerols, cholesterol and non-esterified fatty acids are also present. Sugar-containing lipids, such as cerebrosides, sulphatides and gangliosides are abundantly present. Female parasites contain more lipids, particularly acylglycerols and phospholipids. Acylglycerols, phosphatidyl choline, phosphatidyl ethanolamine and glycolipids incorporate a large amount of radiolabelled precursor substrate in A. galli. The presence of important enzymes of lipid biosynthesis like glucose-6-phosphate dehydrogenase, malate dehydrogenase and hydroxymethyl glutaryl-CoA reductase as well as an enzyme of lipid ester hydrolysis, triacylglycerol lipase is detected in the parasite. These enzymes show subcellular distribution patterns and Michaelis-Menten kinetic characteristics comparable with that from rat liver homogenate. Studies on the uptake of labelled precursor molecules for lipid biosynthesis, glucose, acetate and palmitate show that the parasites can take up the isotopes readily in a time-dependent manner, showing substrate saturation kinetics, dependence upon Na ions, and can be inhibited by the presence of the bile salts sodium cholate and sodium deoxycholate. The substrate affinity constant (Kt) and maximum apparent velocity of glucose uptake in A. galli were found to be 9.09 mM and 26.67 mM per 100 mg tissue dry weight per min at 37 degrees C.