Mammalian Choline Dehydrogenase Is a Quinoprotein

Abstract

Mammalian choline dehydrogenase (EC 1.1.99.1) has been proved to be a quinoprotein in which pyrroloquinoline quinone (PQQ) is involved as the prosthetic group. The enzyme was purified from dog liver mitochondria by solubilizing the enzyme with Brij 58 and chromatographically separating it almost to homogeneity. The absorption spectrum of mammalian choline dehydrogenase indicated the presence of PQQ with a typical shoulder at 320 nm. Since PQQ was attached to the enzyme by a covalent linkage, the chromophore was isolated with an acid hydrolysate and the isolated chromophore gave rise the identical spectroscopic characteristics to that obtained from the amine oxidase of Aspergillus niger in which PQQ is covalently linked. The isolated chromophore potently activated apo-D-glucose dehydrogenase (EC 1.1.99.17) supporting the presence of PQQ in mammalian choline dehydrogenase.