CO2 is the inorganic carbon substrate of NADP malic enzymes from Zea mays and from wheat germ

Abstract

NADP malic enzyme (EC 1.1.1.40) was extracted and partially purified from the green leaves of Zea mays var. Felix and from wheat germ. The active inorganic carbon species for both enzymes was, in contrast to an earlier report, CO2not HCO−3. The apparentKm, co2, for the maize enzyme was 1.2 mM and the apparent Km, co2, for the wheat germ preparation was 4.2 mM under conditions of substrate saturation, pH 7.3 and 17°C. These observations support the views that CO2, rather than HCO3− as has been suggested, is produced in bundlesheath chloroplasts and that the reaction mechanism catalysed by plant cytosolic and chloroplastic NADP malic enzymes is similar to that proposed for avian NADP malic enzymes. Copyright © 1987, Wiley Blackwell. All rights reserved