PDF File - The Indian Society for Parasitology

8 Soodparasite of its ATP production (Kaur and Sood, 6-phosphate dehydrogenase (GDPH) and 6-phosphogluconate dehydrogenase, as also the in vitroeffects of TMS and RFX on these enzymes have beenTCA cycle: Studies on aerobic catabolism ofdemonstrated (Kaur and Sood, 1985). GDPH exhibitscarbohydrates in helminthology is an important areaactivity (4 nmoles/min/mg protein) at pH 7.4 and 37º Cof research. In small nematodes, the TCA cycle plays(Kapur et al., 1984). Thermostability of GPDH,an important but not exclusive part in their energyseparately for male and female worms has beeneconomy (Ward, 1982). The occurrence of TCA cyclestudied (Harpreet et al., 1991).in parasites has not been demonstrated with the sameprecision as in vertebrate tissue or bacteria. A Synthesis of nucleic acids in adult H. contortus, is alsofunctional TCA cycle may exist in the developing eggs indicative of the operation of pentose phosphateand larvae of H. contortus. The presence of aerobic pathway (Kapur and Sood, 1986c).enzyme systems in the larvae may be a preparation forthe next stage of development, since development ofAmino acidslarvae to adults requires oxygen. Various enzymes of Amino acids commonly found in proteins, also occurthe TCA cycle viz. aconitase (ACO), isocitrate as free acids. There are number of amino acids whichdehydrogenase (ICDH), succinate dehydrogenase are never found as constituents of proteins, but play(SDH), fumerate reductase (FR), fumarase and malate important metabolic roles. Therefore, it is essential todehydrogenase (MDH) have been detected in adult H. study both free and bound amino acids.contortus (Kaur and Sood, 1983c). Low activities ofACO and ICDH suggest that TCA cycle has a minor Composition: In adult H. contortus, both free andfunction and the pathway of CO fixation is the major bound acids are present (Kapur and Sood, 1984b). The2pathway in the energy metabolism of the parasite. level of free amino acids is 191 mg in male and 523 mgIncorporation of carbon into proteins and in female per 100 g on fresh weight basis. Various14carbohydrates (Kapur and Sood, 1986c). and of C acids in free form include aspartic acid (Asp),into various amino acids (Kapur and Sood, 1984b), glutamic acid (Glu), leucine + isoleucine (Leu+Ile),also give evidence for the TCA cycle operation in H. tryosine (Try), lysine+histidine (Lys+His),contortus.glycine+serine (Gly+Ser), arginine (Arg),valine+methionine (Val+Met), cystine+cysteineIn a study on the effects of pH and temperature, Kapur (Cys-Cys+Cys), β-alanine (Ala) and α−Ala inet al. (1984), found that SDH exhibits maximum decreasing order of concentration in female, and inactivity (about 120 nmoles/ min/mg protein) at anmale, the order of occurrence is: Asp>Glu>Tyr>βoptimumpH of 8.2 and temperature 32° C. pHAla>Lys+His>Gly+Ser>Leu+Ile>Val+Met>Agr.optimum for ICDH (about140nmoles/min/mgThus, in male Cys-Cys+Cys and α−Ala are missing. Inprotein) and MDH (about 30 nmoles/min/mg protein)female, concentration of Leu, Ile and Asp isis 9.0 and 7.8 respectively; optimum temperaturesignificantly higher than in male, and in male it is ofbeing 32º C for both the enzymes (Kapur et al., 1985).Tyr, β−Ala, Lys+His and Glu. However, concentrationThe in vitro effects of TMS and RFX on various of Val, Met, Gly, Ser and Arg is similar in both theenzymes at 50 µg/ml, have shown varying degrees of sexes. Asp is present in the highest concentration ininhibition of SDH and FR. At the same concentration, both the sexes and the acid, in least concentration isthe activities of other enzymes remained unaltered Arg in male and α-Ala in female. Like other(Kaur and Sood, 1983c). Also, the in vitro effects of invertebrates, in H. contortus too, free amino acidNLZ, ABZ, NLV, NLF, TP and FBZ have been studied pools are dominated by one or two amino acids, i.e.,on LDH (Kaur and Sood, 1993).Asp in female and Asp, Glu in male. Proline (Pro) notreported has been earlier demonstrated by NigamPentose phosphate pathway: This is an alternative (1979). Higher amount of Met in female than in malepathway of glucose catabolism. There is, however, no indicates the extent of transaminase reactions. Moredefinite evidence that this pathway is involved in of Lys in male in indicative of its role in maintainingenergy metabolism in parasitic nematodes. Its main sperm viability (having a histone-like function) as infunction may be to provide NADPH and C 5 and C 7 humans. As in birds, more of Glu in male may play asugars for synthetic reactions (Barrett, 1976). In H. role in the maintenance of osmolarity and pH ofcontortus, key enzymes of this pathway, viz. glucose- seminal plasma.