Biosynthesis of Porphyrinogens in Etiolated Euglena gracilis Z. I. Isolation and Purification of an Endogenous Factor Stimulating the Formation of Porphyrinogens

A low molecular weight, heat-stable factor has been purified from Euglena gracilis supernatant fraction by employing gel filtration, cation and anion exchange and paper chromatography. This endogenous compound stimulates porphobilinogenase (PBG-ase) (EC 4.3.1.8) activity, an enzyme of the porphyrin biosynthetic pathway. 1CT M folic acid and ICI" M 6-biopterin produced a significant activation, equivalent to 2—4 units of the purified factor. Elution patterns from the columns and fluorescence and UV absorption peaks suggest that this compound is a pteridine. This conclusion is further supported by the fact that both, folic acid and 6-biopterin can replace the action of the isolated factor on PBG-ase. The mechanism of stimulation is discussed.