Description
This enzyme is a member of the 'AdoMet radical' (radical SAM) family, all members of which produce the 5'-deoxyadenosin-5'-yl radical and methionine from AdoMet [i.e. S-adenosylmethionine, or S-(5'-deoxyadenosin-5'-yl)methionine], by the addition of an electron from an iron-sulfur centre. The radical is converted into 5'-deoxyadenosine when it abstracts a hydrogen atom from C-6 and C-8, leaving reactive radicals at these positions so that they can add sulfur, with inversion of configuration. This enzyme catalyses the final step in the de-novo biosynthesis of the lipoyl cofactor, with the other enzyme involved being EC 2.3.1.181, lipoyl(octanoyl) transferase. Lipoylation is essential for the function of several key enzymes involved in oxidative metabolism, as it converts apoprotein into the biologically active holoprotein. Examples of such lipoylated proteins include pyruvate dehydrogenase (E2 domain), 2-oxoglutarate dehydrogenase (E2 domain), the branched-chain 2-oxoacid dehydrogenases and the glycine cleavage system (H protein). An alternative lipoylation pathway involves EC 2.7.7.63, lipoate-protein ligase, which can lipoylate apoproteins using exogenous lipoic acid (or its analogues).
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