抄録
Rat hepatic uroporphyrinogen III co-synthase was isolated and purified 73-fold with a 13% yield by (NH_4)_2SO_4 fractionation and sequential chromatography on DEAE-Sephacel, Sephadex G-100 (superfine grade) and folate-AH-Sepharose 4B. The purified co-synthase has an M_r of approx. 42000, and is resolved into two bands, each possessing co-synthase activity, by polyacrylamide-gel electrophoresis. A factor was dissociated from the purified co-synthase. Results of both microbiological and competitive protein-binding assays suggest that it is a pteroylpolyglutamate. The isolated pteroylpolyglutamate factor was co-eluted with authentic N^5-methyltetrahydropteroylheptaglutamate on DEAE-Sephacel. Uroporphyrinogen III is formed by co-synthase-free preparations of uroporphyrinogen I synthase in the presence of tetrahydropteroylglutamate. Tetrahydropteroylheptaglutamate is also able to direct the formation of equivalent amounts of uroporphyrinogen III at a concentration approximately one-hundredth that of tetrahydropteroylmonoglutamate. These results suggest that a reduced pteroylpolyglutamate factor is associated with rat hepatic uroporphyrinogen III co-synthase, and that this may function as a coenzyme for the biosynthesis of uroporphyrinogen III.
