Glyconeogenesis, Krebs Cycle Intermediates and Enzymes during Embryogenesis of the Camel Tick, Hyalomma dromedarii (Acarina: Ixodidae)
Hamed, Ragaa R.; Fahmy, Afaf S.; Kamel, Mamdouh Y.
The TC-A cycle enzymes and intermediates were examined in eggs of Hyalomma dromedarii (Koch 1844). Unlike insects α-ketoglutarate and not citrate is the major carboxylic acid accumulated. The decrease in α-ketoglutarate and proline at the late stage of embryogenesis coincide with the abrupt increase in glutamate-pyruvate and glutamate-oxaloacetate transaminases and NAD (P) malic enzymes, suggested the possible role of malic enzyme and the transaminases in disappearance of a-ketoglutarate. The specific activities of TC-A cycle enzymes, citrate synthase, aconitase, isocitrate dehydrogenase (IC-DH), succinate dehydrogenase (S-DH), fumarase and malate dehydrogenase (M-DH) were followed during embryogenesis. The TC-A cycle is characterized by the low level of S-DH and the possible operation of M-DH in the reversed direction (oxaloacetate - malate). The low activity of the TC-A cycle enzymes and the operation of the aspartate-malate cycle suggested the biosynthetic role of the TC-A cycle in developing eggs. The specific activities of fructose 1,6-bisphosphatase and phosphoenol pyruvate (PE-P) carboxykinase at late stage of embryogenesis were reported. The functional significance of the operation of the TC-A, glyoxylate, aspartate-malate cycles under low oxygen conditions and the presence of fructose 1,6-bisphosphatase and PE-P carboxykinase in relation to glycogenesis is discussed.