Dirofilaria immitis: comparison of cytosolic and mitochondrial glutamate dehydrogenases.

Two membrane-bound glutamate dehydrogenases were found in adult Dirofilaria immitis, an NAD-linked enzyme (EC 1.4.1.2) in the cytosol (C-GDH) and an enzyme equally reactive with NAD or NADP (EC 1.4.1.3) in the mitochondria (M-GDH). The cytosolic enzyme had a pH optimum of 7.8-8.0 and exhibited 30% more activity at 25 C than at 37 C (pH 8.0). The mitochondrial enzyme had a pH optimum at 8.4 and exhibited 27% more activity at 37 C than at 25 C (pH 8.4); it was also more sensitive to heat denaturation. Gel filtration of worm subfractions separated four peaks of C-GDH activity with molecular weights of approximately 610, 285, 180, and less than 100 thousand, and a single major peak of M-GDH activity with a molecular weight of about 335,000. When assayed at pH 8, 37 C, and 200 microM NADH, the Km for the substrate, alpha-ketoglutarate, was equivalent for the two enzymes, but the Km for ADP (activator) was five times greater for M-GDH. When the two enzymes were assayed at pH 8.0, 37 C, and 100 microM NADH, 1 mM ADP approximately doubled and 1 mM ATP halved the velocity observed for each enzyme with no effector present. Under these assay conditions AMP, IDP, GDP, and GTP had opposite effects on the reaction velocities for the two enzymes. When the assay conditions were changed, the effects of added purine nucleotides varied, even directionally. Addition of up to 5 mM glutamate (product) had no significant effect on C-GDH kinetics, nor on the substrate Km of M-GDH.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxidative decarboxylation reactions in Dirofilaria immitis glucose metabolism.

1. Malic enzyme (EC 1.1.1.39) activity was demonstrated in the mitochondrial fraction of dog heartworm extracts. 2. Data published earlier together with those presented here confirm the presence of all the enzymes of the pentose shunt. 3. 14C from uniformly labelled glucose was incorporated into the nucleic acids, and methylene blue increased production of xylose-5-phosphate and of 14CO2 from [1-14C]glucose indicating a functioning pathway. 4. The oxidative decarboxylation of malate and of 6-phosphogluconate may account for the observed labelled CO2 formed when labelled glucose is metabolized since a functional tricarboxylic acid cycle is doubtful in this parasitic helminth.

Mesocestoides (Cestoda) in a child in Mississippi treated with paromomycin sulfate (humatin).

The fifth case of human infection with Mesocestoides in the United States is reported in a 17-month-old child living in Mississippi. The child was asymptomatic and the source of the infection in unknown. Stools examined after treatment with paromomycin sulfate (Humatin) revealed no further evidence of infection. This is the 18th case of Mesocestoides infection in man reported in the literature.

Glycerol metabolism in the adult dog heartworm, Dirofilaria immitis.

1. When adult Dirofilaria immitis were incubated up to 60 min in a medium containing physiological concentrations of glycerol and glucose, the mean amount of free glycerol present did not change significantly. 2. [14C]2-glycerol disappeared from media in which 1 g heartworms were incubated at a linear rate of about 0.7 mumol/hr/g during the first hour. 3. 85-95% of the radioactivity in the Folch extract remained in the aqueous phase. 4. Phosphoglycerides and diacylglycerols accounted for better than 90% of the 14C in the lipids. 5. The rate of glycerol conversion to lactate was only about 0.02% of the rate of glucose conversion under experimental conditions. 6. The data indicate that, although dog heartworms do utilize glycerol as a substrate in glycolysis, it is probably of more importance in lipid synthesis.

Lipid synthesis in the adult dog heartworm, Dirofilaria immitis.

1. Incorporation studies with three labelled substrates--[14C]2-glycerol, [14C]1-acetate and [14C]1-oleic acid--demonstrated that adult dog heartworms can synthesize all classes of complex lipids present, including free cholesterol. 2. Diacylglycerols and phosphoglycerides were most rapidly labelled regardless of the precursor employed. 3. 14C from glycerol was found in the aqueous phase of saponified lipids, whereas that from oleic acid was in the fatty acid portion. 4. Tag from acetate was predominantly in the fatty acid portion of saponified lipids and also occurred in the unesterified fatty acids. 5. Acetate and unesterified fatty acids, as represented by oleic acid, were more readily used for lipid synthesis than was glycerol.

Glycolytic end products of the adult dog heartworm, Dirofilaria immitis.

1. Adult dog heartworms remained alive and motile for 24 hr without oxygen present and with only glucose available as a substrate. 2. Lactate accounted for 55% of the carbon from the 1-14C-glucose utilized in 1 hr and 14CO2 for 1.9%. 3. Only traces of 14C were found in glycogen and no net accumulation of acetate was demonstrated. 4. Dirofilaria immitis resembles Litomosoides carinii in the percent of utilized glucose appearing as lactate but is more akin to Brugia pahangi and Dipetalonema viteae in survival under anaerobic conditions and in negligible acetate production.

Hexokinase of the adult dog heartworm, Dirofilaria immitis.

1. Dirofilaria immitis hexokinase was relatively heat stable and had a pH optimum range between 7.8 and 8.2. 2. Mean Vmax was 0.40 +/- 0.10 (S.D.) mumole/min/100 mg of worm. 3. Mean Km values were 0.32 mM for glucose, 0.86 mM for fructose and 0.39 mM for ATP. 4. Glucose-6-phosphate was not a strong product inhibitor. 5. Starch gel electrophoresis demonstrated at least three isozymes.