Properties of Choline Oxidase of Cylindrocarpon didymum M-1

Choline oxidase from the cell-free extract of Cylindrocarpon didymum M-1 showed a molecular weight of 120,000 by the gel filtration method and 145,000 by the sedimentation velocity method. The enzyme exhibited an absorption spectrum characteristic of a flavoprotein with absorption maxima at 276, 370 and 454 nm and a shoulder at 470 nm. Anaerobic addition of choline as well as sodium dithionite to the enzyme produced a disappearance of the peak at 454 nm.

Choline oxidase consists of two identical subunits, which have a molecular weight of 64,000, and contains two mol of FAD per mol of enzyme. The flavin was shown to be covalently bound to the protein.

The enzyme was inactivated by Ag⁺, Hg²⁺, Cu²⁺ and Zn²⁺. The enzyme oxidized choline, betaine aldehyde and N, N-dimethylaminoethanol and apparent Km values were 1.3 mm, 5.8 mm and 14 mm, respectively.