The oxidation of cyst(e)ine by mast-cell tumour P815 in culture

1. Mast-cell tumour P815 cells oxidize (35)S]cyst(e)ine to (35)SO(4) (2-). 2. Addition of cysteinesulphinate or sulphite decreases the formation of (35)SO(4) (2-); at the same time (35)S]cysteinesulphinate or (35)SO(3) (2-) accumulates. 3. Extracts of P815 cells form sulphite from cysteinesulphinate and 2-oxoglutarate. The K(m) for cysteinesulphinate is 6.35mm and that for 2-oxoglutarate is 0.165mm. 4. Extracts oxidize sulphite to sulphate. 5. No formation of hydrogen sulphide from cyst(e)ine was detectable. 6. It is concluded that P815 cells oxidize cyst(e)ine to sulphate solely via cysteinesulphinate and sulphite. 7. The concentration of the enzymes catalysing this sequence is unaltered by several variations in the conditions of growth.