Alcohol oxidases of Kloeckera sp. and Hansenula polymorpha. Catalytic properties and subunit structures

1. Alcohol oxidase (alcohol: oxygen oxidoreductase) of a thermophilic methanol-utilizing yeast, Hansenula polymorpha DL-1, was isolated in crystalline form. 2. This alcohol oxidase of H. polymorpha was more stable to heat than was the enzyme of Kloeckera sp. This difference in heat stability is compatible with the difference in growth temperatures for both yeasts. 3. The crystalline alcohol oxidases of both yeast oxidized the lower primary alcohols (C-2 to C-4) as well as methanol. The apparent Km values for the methanol of Kloeckera and H. polymorpha enzymes were 0.44 and 0.23 mM, respectively. The enzymes could also oxidize formaldehyde to formate, and were inactivated by relatively low concentrations of hydrogen peroxide. 4. The molecular weight for both enzymes was calculated to be about 670000. Each enzyme is composed of eight identical subunits (molecular weight 83000) and contains eight moles of FAD as the prosthetic group. The NH2-terminal and COOH-terminal amino acids of H. polymorpha enzyme were identified as alanine and phenylalanine, respectively. The octameric subunits model of each enzyme was confirmed by electron micrographs, which showed an octad aggregate, composed of two tetragons face to face.