Biochemical Differences between Embryonic and Larval Cytoplasmic and Mitochondrial Malate Dehydrogenases of Hyalomma dromedarii (Acarina: Ixodidaer)
Hamed, Ragaa R; Mamdouh, Kamel Y; Fahmy, Afaf S
2 activities of cytoplasmic (c1-MDH and c2-MDH) and mitochondrial malate dehydrogenase (m-MDH) of Hyalomma dromedarii (Koch 1844) eggs and larvae were measured electrophoretically and chromatographically during development: The electrophoretic mobility of larval C1 and m-MDH differs from that of the developing embryo. The m-MDH is predominant after age 9 days, representing 65 % of the total activity. While the embryonic and larval m-MDH have a similar pH optimum of 8.6, the pH optima for their c1-MDH are 8 and 7.5 respectively. The Km values for oxaloacetate reduction from both sources are almost similar for the m-MDH (4.2 and 4.3 x 10-5 M) and the c1-MDH (7.6 and 8 x 10-5 M). The Km values for NADH of embryonic and larval c1-MDH are 5 x 10-5 and 1.4 x 10-4, respectively. - Inhibition by high concentrations of oxaloacetate was examined: While larval c1-MDH is not affected, embryonic and larval m-MDH and embryonic c1-MDH are strongly inhibited with Kj values of 2.7, 2.75 and 3.9 mM, respectively. The inhibition of embryonic and l₁arval m-MDH increases by lowering the pH, indicating the formation of an abortive binary complex. However, inhibition of embryonic c1-MDH is not affected by pH. Similarities and differences between the c1-MDH and m-MDH of embryonic and larval enzymes with the corresponding enzymes from different sources were discussed.