The glyoxylate cycle, a variation of the
tricarboxylic acid cycle, is an
anabolic pathway occurring in
plants,
bacteria,
protists, and
fungi. The glyoxylate cycle centers on the conversion of
acetyl-CoA to
succinate for the synthesis of
carbohydrates. In microorganisms, the glyoxylate cycle allows cells to utilize simple carbon compounds as a carbon source when complex sources such as
glucose are not available. The cycle is generally assumed to be absent in animals, with the exception of
nematodes at the early stages of embryogenesis. In recent years, however, the detection of
malate synthase (MS) and
isocitrate lyase (ICL), key enzymes involved in the glyoxylate cycle, in some animal tissue has raised questions regarding the evolutionary relationship of enzymes in
bacteria and
animals and suggests that animals encode alternative enzymes of the cycle that differ in function from known MS and ICL in non-metazoan species.