The presence of isocitrate lyase activity in the southern army worm, Prodenia eridania (Cramer)

Biochemical studies of tick embryogenesis. V. Purification and partial characterization of isocitrate lyase from eggs of the tick Hyalomma dromedarii

1. Isocitrate lyase (Ds-isocitrate glyoxylate-lyase, EC 4.1.3.1) was purified approximately 93-fold from developing embryos of the tick Hyalomma dromedarii. 2. The enzyme requires Mg2+ (Km 2.1 mM) and sulfhydryl compounds for maximal activity and has a pH optimum of 7.4 in phosphate buffer. The Km of the enzyme for isocitrate is 2.4 mM. 3. Data obtained from the pH effect on Km implicate the presence of at least three dissociable groups with pK's of 5.8, 6.8 and 7.4 involved in the enzyme catalysis. 4. At the optimal pH the enzyme is competitively inhibited by oxaloacetate (Ki 0.7 mM) and pyruvate (Ki 0.63 M), noncompetitively inhibited by acetyl-CoA (Ki 1.6 mM) and succinate (Ki 1.35). 5. Inhibition by phosphoenolpyruvate in pH-dependent. The enzyme is noncompetitively inhibited by phosphoenolpyruvate at pH 4.4 (Ki 1.33 mM), 5.6 (Ki 1.7 mM) and pH 8 (Ki 1.36 mM), and competitively inhibited at pH 6.5 (Ki 1.58) and 6.8 (Ki 3.0 mM). 6. The results suggest the regulation of H. dromedarii isocitrate lyase activity during embryonic development by variations in the differential rate of enzyme synthesis an in the intracellular levels of certain metabolites.

Cell remodeling in the fat body of an insect

The fat body of the Lepidopteran, Calpodes ethlius, undergoes major functional changes during larval-adult metamorphosis. These changes occur in conjunction with extensive cell remodeling - a process whereby one population of cellular organelles is destroyed and replaced by another during development. Fat body organelles including mitochondria, microbodies, and RER are destroyed on a massive scale shortly before pupation (Locke and Collins, 1965; Locke and McMahon, 1971) a new populations of each are regenerated shortly after emergence of the adult. In addition, protein, lipid and RNA reserves formed shortly before pupation and multivesicular bodies formed shortly before emergence are secreted into the haemocoel during the first few days of adult life. Electron microscopic studies using tracer techniques, cytochemical and enzyme localization procedures, and sterological analyses have been undertaken to determine the time course and mechanism of organelle regeneration and the fate of reserves stored in the fat body.