title: The formation of exchangeable sulphite from adenosine 3'-phosphate 5'-sulphatophosphate in yeast.
abstract: A new low-molecular-weight bound sulphite was found in yeast enzyme reaction systems which convert the sulphur of 35S-labelled adenosine 3'-phosphate 5'-sulphatophosphate into exchangeable radioactive sulphite. This bound sulphite was separated from other components by paper electrophoresis and Sephadex G-25 chromatography, and shown to be a peptide with multiple thiol groups and an estimated mol.wt. of 1400. The labelled sulphur in this peptide is highly exchangeable with unlabelled sulphite, but exchangeability decreases with time and freeze-drying. The low-molecular-weight acceptor is tightly bound to enzyme B of the yeast system and, apparently, accepts the sulpho group of adenosine 3'-phosphate 5'-sulphatophosphate and is released as bound sulphite only in the presence of enzymically or chemically reduced fraction C. It is proposed that the low-molecular-weight acceptor is a carrier peptide which, after release of the reduced sulphur, becomes re-oxidized and returns to enzyme B. Fraction C appears to function as an obligatory reductant of the oxidized acceptor before it can accept another-SO-3-moiety from adenosine 3'-phosphate 5'-sulphatophosphate. These findings are consistent with mechanisms proposed for sulphate reduction in spinach and Chlorella, and suggest that fraction C is the natural thiol required in these systems. An improved column technique for the preparation of adenosine 3'-phosphate 5'-sulphatophosphate is described.
mesh_terms: D000227:Adenine Nucleotides / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002850:Chromatography, Gel; D004586:Electrophoresis; D005459:Fluorides / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D008954:Models, Biological; D008970:Molecular Weight; D010724:Phosphoadenosine Phosphosulfate / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000378:metabolism*; D013447:Sulfites / Q000302:isolation & purification / Q000378:metabolism*; D013462:Sulfur Radioisotopes; D013466:Sulfurtransferases / Q000378:metabolism; D013997:Time Factors
chemical_list: D000227:Adenine Nucleotides; D002352:Carrier Proteins; D013447:Sulfites; D013462:Sulfur Radioisotopes; D010724:Phosphoadenosine Phosphosulfate; D013466:Sulfurtransferases; D008274:Magnesium; D005459:Fluorides