Properties of an arylalkylamine N-acetyltransferase from the nematode, Ascaridia galli

Xenobiotic metabolizing enzymes and metabolism of anthelminthics in helminths

Anthelminthics remain the only accessible means in the struggle against helminth parasites, which cause significant morbidity and mortality in man and farm animals. The treatment of helminthic infections has become problematic because of frequent drug resistance of helminth parasites. The development of drug resistance can be facilitated by the action of xenobiotic metabolizing enzymes (XMEs). In all organisms, XMEs serve as an efficient defense against the potential negative action of xenobiotics. The activities of XMEs determine both desired and undesired effects of drugs, and the knowledge of drug metabolism is necessary for safe, effective pharmacotherapy. While human and mammalian XMEs have been intensively studied for many years, XMEs of helminth parasites have undergone relatively little investigation, so far. However, many types of XMEs, including oxidases, reductases, hydrolases, transferases, and transporters, have been described in several helminth species. XMEs of helminth parasites may protect these organisms from the toxic effects of anthelminthics. In case of certain anthelminthics, metabolic deactivation was reported in helminth larvae and/or adults. Moreover, if a helminth is in the repeated contact with an anthelminthic, it defends itself against the chemical stress by the induction of biotransformation enzymes or transporters. This induction can represent an advantageous defense strategy of the parasites and may facilitate the drug-resistance development.

Neurogenetics of vesicular transporters in C. elegans

The nematode Caenorhabditis elegans has a number of advantages for the analysis of synaptic molecules. These include a simple nervous system in which all cells are identified and synaptic connectivity is known and reproducible, a large collection of mutants and powerful methods of genetic analysis, simple methods for the generation and analysis of transgenic animals, and a number of relatively simple quantifiable behaviors. Studies in C. elegans have made major contributions to our understanding of vesicular transmitter transporters. Two of the four classes of vesicular transporters so far identified (VAChT and VGAT) were first described and cloned in C. elegans; in both cases, the genes were first identified and cloned by means of mutations causing a suggestive phenotype (1, 2). The phenotypes of eat-4 mutants and the cell biology of the EAT-4 protein were critical in the identification of this protein as the vesicular glutamate transporter (3, 4). In addition, the unusual gene structure associated with the cholinergic locus was first described in C. elegans (5). The biochemical properties of the nematode transporters are surprisingly similar to their vertebrate counterparts, and they can be assayed under similar conditions using the same types of mammalian cells (6, 7). In addition, mild and severe mutants (including knockouts) are available for each of the four C. elegans vesicular transporters, which has permitted a careful evaluation of the role(s) of vesicular transport in transmitter-specific behaviors. Accordingly, it seems appropriate at this time to present the current status of the field. In this review, we will first discuss the properties of C. elegans vesicular transporters and transporter mutants, and then explore some of the lessons and insights C. elegans research has provided to the field of vesicular transport.

Purification and characterization of prostaglandin-H E-isomerase, a sigma-class glutathione S-transferase, from Ascaridia galli

Comparison of partial primary sequences of sigma-class glutathione S-transferases (GSH) of parasitic helminths and a GSH-dependent prostaglandin (PG)-H D-isomerase of rat immune accessory cells suggested that some of the helminth enzymes may also be involved in PG biosynthesis [Meyer and Thomas (1995) Biochem. J. 311, 739-742]. A soluble GSH transferase of the parasitic nematode Ascaridia galli has now been purified which shows high activity and specificity in the GSH-dependent isomerization of PGH to PGE, comparable to that of the rat spleen enzyme in its isomerization of PGH to PGD, and similarly stimulates the activity of prostaglandin H synthase. The enzyme subunit is structurally related to the rat spleen enzyme and sigma-class GSH transferases of helminths according to the partial primary sequence. The data support the hypothesis that some sigma-class GSH transferases of helminth parasites are involved in PG biosynthesis which, in the case of PGE, is likely to be associated with the subversion or suppression of host immunity. A PG-H E-isomerase of comparable specificity and activity has not previously been isolated.