RESUMO
Phosphoglucoisomerase from cytosol of immature wheat endosperm was purified 650-fold by ammonium sulphate fractionation, isopropyl alcohol precipitation, DEAE-cellulose chromatography and gel filtration through Sepharose CL-6B. The enzyme, with a molecular weight of about 130,000, exhibited maximum activity at pH 8·1. It showed typical hyperbolic kinetics with both fructose 6-P and glucose 6-P with Km of 0·18 mM and 0·44mM respectively. On either side of the optimum pH, the enzyme had lower affinity for the substrates. Using glucose 6-P as the substrate, the equilibrium was reached at 27% fructose 6-P and 73% glucose 6-P with an equilibrium constant of 2·7. The ΔF' calculated from the apparent equilibrium constant was +597 cal mol–1 . The activation energy calculated from the Arrhenius plot was 5500 cal mol–1. The enzyme was completely inhibited by ribose 5-P, ribulose 5-P and 6-phosphogluconate, with Ki values of 0·17, 0·25 and 0·14 mM respectively. The probable role of the enzyme in starch biosynthesis is discussed.
RESUMO
The ontogeny of hexokinase, phosphofructokinase, phosphoglucoisornerase, aldolase, pyruvate kinase and lactate dehydrogenase activities which are associated with glycolysis, an important energy yielding process, has been studied in human fetal heart for periods ranging from 13 weeks to above 33 weeks of gestation. Hexokinase, phosphoglucoisomerase and pyruvate kinase activities show similar developmental profiles exhibiting maximum activity at 25-28 weeks ofgestation. Phosphofructokinase activity, on the other hand, shows a minimum at this period and exhibits a peak value at early stages (13-16 weeks of gestation). Though considerable activity for aldolase is observed at an early period, it declines thereafter, but again increases in the later period. The probable role and correlations of these glycolytic enzymes with energy demand and general functional development in human fetal heart in ontogeny are evaluated.