L(+)‐lactate dehydrogenases from <i>Hymenolepis diminuta</i> (Cestoda)

Abstract

Abstract Properties of L( + )‐lactate dehydrogenases from infective eggs, cysticercoids, immature proglottids (anteriors), and pre‐patent (seven day) infections of H. diminuta were studied. Fractionation of isozymes by disc gel and cellulose acetate electrophoresis was unsatisfactory, but some fractionation was obtained by electrofocusing. Other evidence suggested that one form of LDH predominated in eggs and cysticercoids, and a second form in anteriors and pre‐patent worms. The first form was relatively resistant to thermal inactivation and was only slightly inhibited by pyruvate. The second resembled LDH−1 of mammals in being strongly inhibited by pyruvate, even though it occurred in life cycle stages that require no oxygen for grbwth and differentiation. In all tissues K m (lactate) was about 50–100 × K m (pyruvate), but K m (pyruvate) was much higher in eggs and cysticercoids (2.8 × 10 −4 ) than in anteriors and pre‐patent worms (2.8 × 10 −5 mole/li). Energies of activation were 8,419, 13,870, 16,107, and 22,633 cal/mole in cysticercoids, eggs, pre‐patent worms, and anteriors, respectively. In eggs and cysticercoids K m (pyruvate) passed through a minimum at 20−25°C, suggesting that LDH in these tissues may function efficiently at normal environmental temperatures. Anteriors and pre‐patent worms did not exhibit such a correlation.