Model studies on calcium-containing quinoprotein alcohol dehydrogenases. Catalytic role of Ca2+ for the oxidation of alcohols by coenzyme PQQ (4,5-dihydro-4,5-dioxo-1H-pyrrolo(2,3-f)quinoline-2,7,9-tricarboxylic acid)

The catalytic role of calcium ions for the oxidation of alcohols by coenzyme PQQ (4,5-dihydro-4,5-dioxo-1H-pyrrolo(2,3-f)quinoline-2,7,9-tricarboxylic acid) was investigated. The trimethyl ester of PQQ was synthesized by esterification of the coenzyme in methanol to demonstrate the methanol oxidation by the calcium complex of PQQ as well as the redox mechanism of the calcium-containing quinoprotein alcohol dehydrogenases. The addition-oxidative elimination mechanism through the C-5 hemiacetal intermediate is proposed.