Cysteinyl-cysteine and the microsomal protein from which it is derived act as reducing cofactor for prolyl...

Microsomes from L-929 cells contain a reductant which can replace ascorbate as a cofactor for prolyl hydroxylase. The cofactor was extracted with Triton X-100 and exhibited high and low molecular weight forms on S-300 gel columns. Refiltration or trypsin treatment of high molecular weight cofactor produced additional low molecular weight form. The low molecular weight form was purified by P-2 gel filtration, and Dowex-1 and thin layer chromatography. It is ninhydrin reactive, exhibits reduced and oxidized forms with molecular weights of 240 and 460, respectively, and yielded cystine upon acid hydrolysis. The results suggest that it is a dipeptide, cysteinyl-cysteine, derived from a microsomal protein which is the high molecular weight cofactor.