Lipoamide Dehydrogenase from bovine intestinal mucosa 

The name "Diaphorase" has been loosely applied to several enzymes which catalyze the oxidation of either β-NADH or β-NADPH in the presence of an electron acceptor such as methylene blue or 2,6-dichlorophenol-indophenol. Many different assay procedures and "units" are used.
Diaphorases which are specific for either β-NADH or β-NADPH are known. The pig heart enzyme of Straub seems to have native diaphorase (β-NADH specific) as well as lipoic and lipoamide dehydrogenase activities. It is reported to be a single protein. However, Massey reports that "diaphorase" is probably a denatured lipoamide dehydrogenase. Pre-incubation of the pig heart preparation with Cu²⁺ reduces the lipoamide dehydrogenase activity and proportionately increases the β-NADH diaphorase activity. In our laboratory, we have demonstrated this copper effect to some degree on the pig heart enzyme, but no appreciable effect was observed on the Clostridium kluyveri or torula yeast preparations. The lipoamide dehydrogenase: diaphorase ratio is a measure of the denaturation.

Sold on the basis of lipoamide dehydrogenase units.

One unit will reduce 1.0 μmole of DL-lipoamide to DL-dihydrolipoamide per min at pH 6.5 at 25 °C.

Suspension in 3.2 M (NH₄)₂SO₄ solution, pH approx. 6.0

ammonium sulfate suspension

NADPH diaphorase, NADH oxidase, NADPH oxidase, and NADPH lipoamide dehydrogenase <1 unit/mg protein

2-8°C

3

C0400, Carmustine

D5540, Diaphorase from Clostridium kluyveri