CATALYTIC PROPERTIES OF NADP-ISOCITRATE DEHYDROGENASE FROM THE MAIZE SCUTELLUM

NADP-specific isocitrate dehydrogenase (E. C. 1.1.1.42) with a specific activity of 34.6 U/mg protein was purified from the maize scutellum. Purification included ammonium sulphate fractionation, ionexchange chromatography on DEAE-Cellulose, gel-filtration of Sephadex G-25 and Toyoperl HW-55, and ultrafiltration under nitrogen pressure. Studies of the reaction kinetics suggested that the complex <<Mn2+ - isocitrate>> is a true substrate of the enzyme. pH optimum for the complex was 8.2 and Km was 10.8 muM for isocitrate, 47.6 mu for NADP and 10.5 mu for Mn2+. Ions of certain metals (Cu2+ and Mg2+) are involved in regulation of the enzyme activity, as well as intermediates of cell metabolism, such as glyoxalate, oxaloacetate, ATP, and ADP.