Studies on the absorption of amino acids by larval tapeworms (Cyclophyllidea: Taenia crassiceps)

Abstract

Larvae of Taenia crassiceps have been shown to absorb L-valine and L-methionine by a process of active transport. Uptake is maximal at about 43 °C and a pH of about neutrality, and concentration against a gradient has been demonstrated. In advanced larvae, the absorption mechanism has been shown to be specific for neutral aliphatic amino acids, with an uncharged amino group in the α-position. Competitive inhibitions of uptake have been demonstrated in the presence of other amino acids.Comparison has been made with a mechanism present in Hymenolepis diminuta for the uptake of neutral amino acids, demonstrated by Read et al. (1963), and the absorption of L-methionine by the two species has been compared in detail.The uptake of valine and methionine by the two types of larvae has been compared in detail: the presence of two types of sites for the uptake of these aminoacids has been suggested.The absorption of the L-isomers of glutamic acid, proline, serine, glycine and leucine has been demonstrated in advanced larvae. Separate mechanisms for the uptake of acidic amino acids, basic amino acids and neutral aromatic amino acids have been suggested.Thanks are due to Professor G. Chapman, in whose department this work was carried out, and to Miss E. Clarry for her willing assistance. We would also like to thank Dr G. Ayrey, of the Queen Elizabeth College Isotope Unit, for his valuable help, especially in the development of a technique for the simultaneous counting of 14C and 3H. The work was supported by a research grant from the Wellcome Trustees, to whom we are most grateful.

Echinococcus granulosus: absorption of cycloleucine and α-aminoisobutyric acid by protoscoleces

“…Some controversy exists concerning proline uptake by metacestodes of Taenia crassiceps. Haynes & Taylor (1968) and Haynes (1970) considered proline absorption to be mediated, but this view has been disputed by Pappas & Read (1973), who concluded that proline uptake was entirely by diffusion. Separate transport loci for imino acids have been described in a number of vertebrate systems (e.g.…”

Molecular characterization of the surface and cyst fluid components of Taenia crassiceps

“…Similarly, in vitro biosynthetic labelling of proteins with radioactive methionine resulted in low incorporation of radioactive label into proteins by T. crassiceps. Haynes & Taylor (1968) showed that during incubation of T. crassiceps metacestodes in the presence of methionine for 1-4 h, less than 1 % of total methionine uptake was incorporated into protein as compared with 12% for glutamic acid. Although methionine is the standard label used for in vitro biosynthetic labelling, glutamic acid may prove to be a more appropriate source of radioactive label for this parasite.…”

Permeability and membrane transport in the larva ofTaenia crassiceps

“…[ 3 H]Proline uptake was not inhibited by unlabelled proline, and [ 14 C]glutamic acid uptake was not inhibited by unlabelled glutamic acid nor by malic acid (Table 2). Malic acid was reported by Haynes & Taylor (1968) to be a very effective inhibitor of glutamic acid uptake by T. crassiceps metacestodes. These data (Table 2) (Figs.…”

“…The insignificant radioactivity associated with both types of larvae from all incubation periods was attributed to non-specific adsorption of inulin to the external surface of larvae. Haynes & Taylor (1968) and Haynes (1970) reported that glutamic acid and proline are transported by advanced larvae of T. crassiceps by systems which were described as specific, with the implication that uptake of these amino acids is specifically mediated rather than occurring by diffusion. Haynes & Taylor (1968) reported that the uptake of glutamic acid was inhibited by aliphatic dicarboxylic acids, i.e.…”

“…The results of several recent investigations of amino acid and protein uptake by Taenia crassiceps larvae are difficult to interpret. Haynes & Taylor (1968) and Haynes (1970) reported active transport of several amino acids by larvae. However, Esch & Kuhn (1971) reported that these larvae were permeable to much larger molecules, i.e.…”