Characterization of amyloplastic phosphohexose isomerase from immature wheat (Triticum aestivum L.) endosperm.
No Thumbnail Available
Date
1990-02-01
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Phosphohexose 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.
Description
Keywords
Citation
Sangwan RS, Singh R. Characterization of amyloplastic phosphohexose isomerase from immature wheat (Triticum aestivum L.) endosperm. Indian Journal of Biochemistry & Biophysics. 1990 Feb; 27(1): 23-7