Isocitrate Lyase - Biological Function

Biological Function

The ICL enzyme has been found to be functional in various archaea, bacteria, protists, plants, fungi, and nematodes. Although the gene has been found in genomes of nematodes and cnidaria, it has not been found in the genomes of placental mammals.

By diverting isocitrate from the TCA cycle, the actions of ICL and malate synthase in the glyoxylate cycle result in the net assimilation of carbon from 2-carbon compounds. Thus, while the TCA cycle yields no net carbon assimilation, the glyoxylate cycle generates intermediates that can be used to synthesize glucose (via gluconeogenesis), and other biosynthetic products. As a result, organisms that use ICL and malate synthase are able to synthesize glucose and metabolic intermediates from acetyl-CoA derived from acetate or from the degradation of ethanol, fatty acids or poly-β-hydroxybutyrate.

This function is especially important for higher plants which use oilseeds. In these germinating seeds, the breakdown of oils generates acetyl-CoA. This serves as a substrate for the glyoxylate cycle, which generates other cyclic intermediates and serves as a primary nutrient source prior to the production of sugars from photosynthesis.