Theoretical approaches to D-amino acid oxidase.

Several substrates and roles have been proposed for D-amino acid oxidase (E.C. 1.4.3.3.); however, there is no proof that they possess the required characteristics to account for the ubiquity, large amounts and great activity of the enzyme as found in diverse cells and tissues. Based on the similar stereoposition of identically charged atoms and lateral side chain (R) with respect to the alpha-hydrogen atoms in beta-sheet conformation and in D-amino acids, it is proposed that its substrates may include several membrane-related proteins, partially in beta-sheet conformation, whose alpha-hydrogen atoms would be the real object of D-amino acid oxidase catalysis. A monooxygenase-like enzymatic activity of D-amino acid oxidase with these novel substrates is considered, for which the final products are hypothesized to be protein alpha-carbon hydroxyls resulting from the incorporation of one atom of oxygen into the substrate, the other being reduced to water. Alternatively, it is also proposed that D-amino acid oxidase (and possibly other monooxygenase enzymes) would have a hydroperoxide-synthetase activity. In this case, protein alpha-carbon hydroperoxide and not water, but another reduced molecule, would be the final products. The new enzymatic performances of D-amino acid oxidase and the possible role of its potential final products in redox and other biochemical processes are discussed.