SUBCELLULAR-LOCALIZATION OF QUINATE - OXIDOREDUCTASE FROM PHASEOLUS-MUNGO L SPROUTS

Abstract

Quinate:oxidoreductase (QORase, EC 1.1.1.24) was isolated and purified from etiolated mung bean (Phaseolus mungo L.) sprouts and a monospecific antiserum was raised in rabbit to the homogeneous protein. Highly intact etioplasts were isolated from the same plant material. The stroma of the purified etioplasts was enzymatically characterized. Contamination by cytosol, mitochondria and vacuole was estimated from activities of marker enzymes. QORase activity was localized in the stroma (about 91% for both NAD(+) and NADP(+) as a cofactor). Western blotting and immunoprinting of the stroma proteins revealed a single band that migrated identically with the purified QORase. The results suggest that the QORase is localized predominantly, if not exclusively, in the etioplast stroma. The physiological role of the enzyme is discussed.