Two Isoenzymes of Glucosephosphate Isomerase from Spinach Leaves and Their Intracellular Compartmentation

Publisher Website
Google Scholar
Abstract
From spinach leaves (Spinacea oleracea L.) two isoenzymes of glucosephosphate isomerase can be separated by DEAE‐cellulose ion‐exchange chromatography. Isoenzyme 1 eluting at high ionic strength shows a faster mobility during disc gel electrophoresis than isoenzyme 2 eluting at low ionic strength. For both isoenzymes the pH‐optima and Km‐values were very similar for either direction. However, the Km‐values with glucose‐6‐phosphate as substrate (Km= 8.0 mM and 5.9 mM for isoenzyme 1 and 2, respectively) were 20‐fold higher than with fructose‐6‐phosphate as substrate (Km= 300 μM for both isoenzymes). The molecular weight of both isoenzymes was estimated by sedimentation velocity centrifugation analysis to be 120000. The subcellular distribution reveals that isoenzyme 1 is located within the chloroplasts and isoenzyme 2 in the non‐particulate cell fraction (cytosol).The results give further support to the view that in plants there exist two sets of isoenzymes for the oxidative pentose phosphate cycle, one set located in the chloroplasts, the other one in the non‐particulate cell fraction (cytosol).