The level of activity of the NADP-dependent isocitrate dehydrogenase (ICDH) of E. coli ML308 is controlled by a reversible phosphorylation mechanism during growth on acetate as sole carbon source. Under such conditions the enzymes of the glyoxylate bypass, isocitrate lyase (ICL) and malate synthase are induced. This results in competition between ICDH and ICL for the available isocitrate. To allow efficient use of isocitrate via the glyoxylate bypass ICDH is phosphorylated on a single serine residue per subunit which completely inactivates it. Phosphorylation of ICDH is believed to occur at the NADP+ binding site, and so the enzyme is inactive because it cannot bind its cofactor
