Purification and properties of a new Brevibacterium sterolicum cholesterol oxidase produced by E. coli MM294/pnH10

A gene encoding a cholesterol oxidase from Brevibacterium sterolicum novo sp. ATCC21387 was isolated by an expression cloning method and highly expressed by a recombinant strain Escherichia coli MM294/pnH10. The purified cholesterol oxidase was a typical flavoprotein with a molecular mass of 46.5 kDa, absorption peaks at 280, 360, and 450 nm. Optimum pH and temperature were found at pH 6.5 and 55 degrees C, respectively. The enzyme acted on 3 beta-hydroxysteroids such as cholesterol, pregnenolone, and beta-sitosterol at high rates, but on dehydro-epi-androsterone to a lesser degree. The molecular and catalytic properties were different from those of cholesterol oxidase I, which was initially discovered in B. sterolicum novo sp. ATCC21387. The new enzyme, designated cholesterol oxidase II, was distinguished by its high affinity toward cholesterol (K(m) = 30 micromolar).