Enzyme Activity Measurement for Dihydrolipoyl Dehydrogenase

Creative Enzymes is the leading service provider in the field of enzyme activity measurement. Having tested activities of numerous enzymes in the past few years, Creative Enzymes has accumulated extensive and various experiences to ensure rapid and utmost-quality enzyme activity assay services, including the determination of enzyme activity for dihydrolipoyl dehydrogenase.

Dihydrolipoyl dehydrogenase (EC 1.8.1.4) is a mitochondrial structurally conserved homodimeric flavoprotein, which belongs to the pyridine nucleotide-disulfide oxidoreductase family that is ubiquitous in aerobic organisms. Dihydrolipoyl dehydrogenase catalyzes the oxidation of a dihydrolipoyl residue covalently bound to a component protein and the reverse reaction as follows:

Protein N⁶-(dihydrolipoyl)lysine + NAD⁺ ↔ Protein N⁶-(lipoyl)lysine + NADH + H⁺

Dihydrolipoyl dehydrogenase has been characterized from a wide range of organisms including bacteria, eukarya and archaea. This homodimeric enzyme contains a tightly but non-covalently bound flavin nucleotide molecule, a redox disulfide, and one NAD⁺-binding site in each of its subunit. In plants, dihydrolipoyl dehydrogenase is an important component of several mitochondrial multienzyme complexes closely associated with the tricarboxylic acid (TCA) cycle, namely, the pyruvate dehydrogenase complex (or its isoform 2-oxoglutarate dehydrogenase), the branched chain 2-oxoacid dehydrogenase multienzyme complexes, and the glycine decarboxylase complexes. Therefore, dihydrolipoyl dehydrogenase plays a crucial role in the glycine, serine and threonine metabolism, propanoate metabolism and TCA cycle for energy production.

Unlike the glycine decarboxylase complex, which forms relatively unstable complex, the 2-oxoacid dehydrogenase complexes are stable and made up of three components: E1 subunit (2-oxoacid dehydrogenase), E2 subunit (dihydrolipoyl acyltransferase), and E3 subunit (dihydrolipoyl dehydrogenase). E1 is responsible for the release of CO₂ initially and the reductive acetylation of lipoamide prosthetic groups, which are attached to the oligomeric E2 core assembly with transfer occurring via a α-hydroxyethylidene thiamine diphosphate intermediate. E2 mediates acetyl group transfer from the S-acetyl dihydrolipoamide intermediate to CoA with an FAD-linked E3, catalyzing the re-oxidation of reduced lipoamide prosthetic groups coupled to NADH production.

Figure: The crystal structure of human dihydrolipoyl dehydrogenase complexed to NAD⁺.
PDB: 1ZMC

Dihydrolipoyl dehydrogenase can also use free dihydrolipoate, dihydrolipoamide, or dihydrolipoyllysine as a substrate. It is often termed “diaphorase” for its characteristic flavin moiety and NADH oxidase activity, where the electron acceptor is generally an oxidized dye such as methylene blue. Hence dihydrolipoyl dehydrogenase is thought to function as a pro-oxidant. Additionally, in human, dihydrolipoyl dehydrogenase deficiency has been reported to be a target for therapy for conditions such as Friedreich ataxia and ischemia-reperfusion injury. Thus, it can be seen that dihydrolipoyl dehydrogenase serves as a pivotal enzyme in biological metabolism and medical research. However, the activity assays of this enzyme have not been well developed to achieve a better understanding of this enzyme. Fortunately, Creative Enzymes takes advantage of the most advanced spectrophotometric instruments to accurately measure the enzymatic activity of dihydrolipoyl dehydrogenase. Our services and products are the most trusted and proven in the market, with dedicated marketing and technical support. Your business is positioned to succeed with us.