Cobalamin and folate metabolism in helminths.

Knowledge about the source, metabolism and functions of cobalamins and folates in helminths remains fragmentary. It is likely that all helminths, whether free-living or parasitic, cannot synthesize cobalamins and folates de novo. Folates, but not cobalamins, appear to be ubiquitous in helminths. Of the parasitic helminths that take up free cobalamins in vitro, all but one species showed no uptake of cobalamin bound to transport proteins, although the latter type of cobalamin by far predominates in vivo. Certain free-living and parasitic helminths in vitro and in vivo took up a variety of folyl and antifolyl monoglutamates, but it is not known whether helminths can take up any folyl polyglutamates. Helminths that have any folate-dependent metabolism appear able to produce polyglutamylated forms of the required tetrahydrofolate coenzymes. Helminths that possess a functional cobalamin-dependent pathway from succinyl CoA to propionyl CoA appear able to form the required adenosylcobalamin coenzyme. Only free-living helminths may possess a cobalamin (and 5-methyltetrahydrofolate)-dependent pathway from homocysteine to methionine. It is likely that all helminths possess the 5,10-methylenetetrahydrofolate-dependent pathway from deoxyuridylate to thymidylate. All helminths appear able to salvage purine bases and nucleosides, but 10-formyltetrahydrofolate-dependent de novo purine ribonucleotide synthesis has been demonstrated unequivocally only in nematodes. The primitive parasitic groups of helminths exhibit cobalamin metabolism, whereas the more highly evolved ones seem to have lost the mechanisms for uptake and the associated biochemical pathways utilizing cobalamins.

In vitro cultivation of Dipetalonema viteae third-stage larvae: effect of the gas phase.

The effect of the gas phase on the in vitro growth and development of Dipetalonema viteae (Nematoda: Filarioidea) third-stage larvae obtained from the tick vector and 3 day infections of jirds was examined. Measurements of the oxygen (pO2) and carbon dioxide (pCO2) tensions and the pH in the medium were made for each gas phase. In cultures gassed with 5% carbon dioxide in nitrogen the pO2 was between 32 and 50 mm Hg, the pCO2 ranged from 25 to 40 mm Hg and the pH was between 7.2 and 7.4. This gas phase resulted in the best growth and development of third-stage larvae to the fourth-stage. Survival and development of larvae were decreased in cultures with oxygen tensions less than 20 mm Hg and greater than 50 mm Hg.

Internal transport and metabolism of cobalamin in Spirometra mansonoides (Cestoda) spargana.

The anterior 2 mm of the sparganum of Spirometra mansonoides contained 35 to 48% of the total endogenous cobalamin (Cbl) with only 2 to 4% in the terminal 1 cm. [57Co]cobalamin taken up in the posterior region of spargana was transported directionally to the anterior region and concentrated there resulting in a uniform depletion of [57Co]Cbl along the remaining body length. The anterior 2 mm contained 24% of the sparganum's holo-MMCoAM activity with only 5% in the terminal 1 cm. When head and body preparations were chromatographed on Sephadex G-150 columns eluates from both regions exhibited single peaks of MMCoAM activity at an approximate molecular weight of 150,000 and two peaks of endogenous Cbl. The first Cbl peak cochromatographed with MMCoAM activity and the second Cbl peak eluted at the position of free Cbl. Spargana rapidly converted CN-[57Co]Cbl to hydroxocobalamin (OH-Cbl) and adenosylcobalamin (Ado-Cbl) in vitro. In the head region significant amounts of Ado-Cbl were present (25%) although OH-Cbl was the predominant form of Cbl (45%) after 264 hr in a Cbl-free medium. In the body Ado-Cbl was the predominant form of Cbl (44%) although significant amounts of OH-Cbl were present (27%) after 264 hr in a Cbl-free medium. No methylcobalamin (Me-Cbl) was detected, but an unidentified cobalamin-containing entity (Fraction 4) was present. Based on these results we propose that the sparganum takes up cobalamin, concentrates it in the anterior, "head" region, sequentially metabolizes it to the hydroxyl then the adenosyl forms, and that the adenosylated form is used in this region of high, anaerobic metabolism as an obligatory coenzyme for MMCoAM, in coordination with the differentiation of the sparganum to the adult cestode.

The presence and possible function of methylmalonyl CoA mutase and propionyl CoA carboxylase in Spirometra mansonoides.

Both spargana and adult forms of Spirometra mansonoides were shown to accumulate lactate, succinate, acetate, and propionate upon in vitro incubation. Adults differed markedly from the spargana in that quantitatively the most significant products of the former were acetate and propionate while the latter formed primarily acetate and lactate. The adults accumulated approximately 32 times more propionate than the spargana per gram of tissue. In accord with this propionate formation, propionyl CoA carboxylase and methylmalonyl CoA mutase have been found to be present in both stages of the parasite. As might be predicted, however, the activities of the carboxylase and mutase were 100-fold and 10-fold higher, respectively, in the adults as compared to the larvae. A possible physiological relationship between propionate formation and energy generation is suggested. Accordingly, inorganic 32P was incorporated into ATP upon incubation of methylmalonyl CoA with a homogenate obtained from adult S. mansonoides. Since methylmalonyl CoA mutase requires vitamin B12 coenzyme, a relationship between vitamin B12 content and propionate formation in helminths is suggested.

Metabolic fate of cyanocobalamin taken up by Spirometra mansonoides spargana.

Analysis of tissue from Spirometra mansonoides spargana has shown that cyanocobalamin (vitamin B12) is metabolized to adenosylcobalamin and hydroxocobalamin. No methylcobalamin was detected. When the tissues were examined for enzymes which are known to utilize coenzyme forms of vitamin B12, only methylmalonyl CoA mutase, which requires adenosylcobalamin was found. The enzyme, tetrahydropteroylglutamate methyltransferase, which requires methylcobalamin as a cofactor, was not detected. A sizable portion of the cyanocobalamin taken up was bound to ammonium sulfate-precipitable material, suggesting that the binding substance is a protein. Vitamin B12 taken up by spargana was found to be released in vivo with a biological half-life of about 7 weeks.

Isolation and identification of a cobamide coenzyme from the tapeworm Spirometra mansonoides.

A light-sensitive vitamin B12 derivative has been extracted from the adult cestode, Spirometra mansonoides. This corrinoid was identified as the cobamide coenzyme, adenosylcobalamin, by its chromatographic, chemical, and spectral properties.