title: Sulphydryl oxidase: oxidation of sulphydryl groups and the formation of three-dimensional structure in proteins.
abstract: Sulphydryl oxidase, an enzyme isolated from milk, catalyses the de novo synthesis of disulphide bonds. Thiol groups in amino acids or their derivatives, peptides, and proteins are oxidized; molecular oxygen serves as the electron acceptor and undergoes a two-electron reduction to hydrogen peroxide. Michaelis constants vary considerably amongst various substrates; glutathione is a particularly good substrate. Inhibition studies and oxidation of 1,3-diphenylisobenzofuran suggest a mechanism involving an electron transfer to singlet O2 forming an enzyme-bound hydroperoxy group. Evidence for a direct interaction of the enzyme with horseradish peroxidase was also obtained. Although protein-folding appears to be thermodynamically favoured, rates of spontaneous acquisition of functional three-dimensional structures in disulphide-containing proteins have appeared disturbingly slow. In the presence of sulphydryl oxidase, functional structure is rapidly acquired by both reductively unfolded ribonuclease A and reductively denatured immobilized chymotrypsinogen A as judged by restoration of native fluorescence characteristics and biological activity. Preliminary data suggest that unlike thiol:protein-disulphide oxidoreductase, protein-disulphide isomerase, or GSSG/GSH redox systems, sulphydryl oxidase does not permit a 'reshuffling' of disulphide bonds.
mesh_terms: D000818:Animals; D001572:Benzofurans / Q000037:antagonists & inhibitors / Q000378:metabolism; D002384:Catalysis; D002417:Cattle; D004220:Disulfides / Q000378:metabolism; D006735:Horseradish Peroxidase / Q000378:metabolism; D007700:Kinetics; D008892:Milk / Q000201:enzymology*; D010088:Oxidoreductases / Q000032:analysis* / Q000378:metabolism / Q000494:pharmacology; D011487:Protein Conformation; D050862:Oxidoreductases Acting on Sulfur Group Donors
chemical_list: D001572:Benzofurans; D004220:Disulfides; D006735:Horseradish Peroxidase; D010088:Oxidoreductases; D050862:Oxidoreductases Acting on Sulfur Group Donors; C011238:1,3-diphenylisobenzofuran