Purification and Characterization of Serine Hydroxymethyltransferase from Mitochondria of Euglena gracilis z

Mitochondrial serine hydroxymethyltransferase, l-serine: tetrahydrofolate 5,10-hydroxymethyl-transferase (EC 2.1.2.1), (m-SHMT) was extracted and highly purified from Euglena gracilis z. The specific activity increased from the crude extract with 10% yield up to 580-fold through the following steps: ammonium sulfate fractionation, DEAE-cellulose column chromatography and rechromatography, and affinity chromatography with l-lysine-Sepharose 4B. The molecular weight of the purified m-SHMT was 88,000 by gel filtration through Sephadex G-200, and 44,000 by SDS-PAGE. One mol of the purified enzyme contained two mol of pyridoxal 5′-phosphate (PLP), indicating that the enzyme is a dimer. Characteristics of the enzyme were examined and compared with SHMTs of other origins. The m-SHMT of Euglena gracilis z had l-threonine aldolase activity as did s-SHMT of the same origin in addition to the usual SHMT activity.