Sangwan, R SSingh, R1990-02-012009-05-271990-02-012009-05-271990-02-01Sangwan RS, Singh R. Characterization of amyloplastic phosphohexose isomerase from immature wheat (Triticum aestivum L.) endosperm. Indian Journal of Biochemistry & Biophysics. 1990 Feb; 27(1): 23-7http://imsear.searo.who.int/handle/123456789/26339Phosphohexose isomerase from amyloplasts of immature wheat endosperm was purified 133-fold. The enzyme had a molecular weight of 130 kDa and maximum activity at pH 8.6. It showed normal hyperbolic kinetics for both fructose-6-P and glucose-6-P with Km of 0.12 mM and 0.44 mM, respectively. pH had a great influence on Km for fructose-6-P. Using glucose-6-P as the substrate, the equilibrium was reached at 23% fructose-6-P and 77% glucose-6-P and an equilibrium constant of about 3.0. The delta F calculated from the apparent equilibrium constant was +742 cal.mol-1. The activation energy calculated from the Arrhenius plot was 7450 cal.mol-1. None of the sulphydryl reagents at 2.5 mM concentration inactivated the enzyme. The enzyme was competitively inhibited by 6-phosphogluconate, ribose-5-P and ribulose-5-P with Ki values of 0.18, 0.14, and 0.13 mM, respectively. The probable role of the enzyme in starch biosynthesis in amyloplasts is discussed.engGlucose-6-Phosphate Isomerase --isolation & purificationKineticsSubcellular Fractions --enzymologyTriticum --enzymologyJournal Article