Another Microbial Pathway for Acetate Assimilation

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Science  21 Jan 2011:
Vol. 331, Issue 6015, pp. 294-295
DOI: 10.1126/science.1201252

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Countless students in introductory biochemistry classes have heard the adage “fats burn in the flame of carbohydrates.” It refers to the inability of vertebrates to convert acetyl coenzyme A (acetyl-CoA), an important metabolic molecule, into intermediate compounds that replenish carbon in the citric acid cycle and enable the synthesis of glucose. In contrast, plants and certain bacteria, fungi, and invertebrates have solved this barrier to “anabolism from acetate” by using a variation of the citric acid cycle. This variation is called the glyoxylate cycle, and it allows acetyl-CoA to be used as a replenishing source for carbon in the synthesis of glucose and other important reactions (1). However, a number of acetate-using microorganisms lack one of the signature enzymes involved in the glyoxylate cycle, isocitrate lyase, demonstrating that other pathway(s) for acetate assimilation must exist (24). In 2007, fully 50 years after the discovery of the glyoxylate cycle, investigators revealed the first complete details of one of these alternate pathways (5). Now, on page 334 of this issue, Khomyakova et al. (6) describe yet another acetate-assimilation pathway. It is in a salt-loving (halophilic) microorganism belonging to the Archaea, and incorporates features not seen in previously described pathways.