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

Abstract
Mast-cell tumor P815 [mouse] cells oxidize [35S]cyst(e)ine to 35SO42-. Addition of cysteinesulfinate or sulfite decreases the formation of 35SO42-; at the same time [35S] cysteinsulfinate of 35SO42- accumulates. Extracts of P815 cells form sulfite from cysteinesufinate and 2-oxoglutarate. The Km for cysteinesulfinate is 6.35 mM and that for 2-oxoglutarate is 0.165 mM. Extracts oxidize sulfite to sulfate. No formation of H sulfide from cyst(e)ine was detectable. P815 cells oxidize cyst(e)ine to sulfate solely via cysteinesulfinate and sulfite. The concentration of the enzymes catalysing this sequence is altered by several variations in the conditions of growth.