Embryogenesis and the glyoxylate cycle

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The key catalysts of the glyoxylate cycle, isocitrate lyase (EC 4.1.3.1) and malate synthase (EC 4.1.3.2), have been investigated in a variety of tissues [l-3]. In general, the biological a~im~ation of acetate units or the conversion of fatty acids to carbohydrates requires function of glyoxylate cycle [4-61. For example, the function of this cycle is required for conversion of fat to carbohydrate during germination of fat-rich seedlings [7 1. Moreover, the specific activities of isocitrate lyase and malate synthase are highest in second-stage larvae of the nematode Ascaris lumbricoides at a time when the conversion of lipid to carbohydrate is maximal [ 81. The presence of isocitrate lyase and malate synthase has also been reported in several other nematodes [9&O] including a number of free-living forms [ 1 l-141. Although in recent years scattered information has been published on the biochemistry of larval development of free-living nematodes such as Ykrbatrix aceti [14,15] and Caerzorhabditis ekgans [16], ~formation about the basic bio~ern~t~ is still sketchy. For example, nothing is known about the function of glyoxylate cycle enzymes during embryogenesis, although the presence of high levels of isocitrate lyase in early post-embryonic states of C. elegans [ 161 implies that this enzyme functions during embryogenesis. We now present evidence which supports the function of the glyoxylate cycle during embryogenesis of C. eleguns. AS far as we know, this is the first report implicating the occurrence of the glyoxylate cycle in any embryonic animal tissue.