Catalase activity was analyzed in seven organs of pea (Pisum sativum L.) plants: leaves, seeds, flowers, shoots, whole fruits, pods and roots. Leaves showed the highest activity followed by whole fruits and flowers. Catalase was purified from pea leaf peroxisomes. These organelles were isolated from leaves by differential and sucrose density-gradient centrifugation, and catalase was purified by two steps involving anion exchange and hydrophobic chromatography using a Fast Protein Liquid Chromatography system. Pure catalase had a specific activity of 953 mmol H2O2 min(-1) mg(-1) protein and was purified 1000-fold, with a yield of about 19 microg enzyme per kg of pea leaves. Analysis by SDS-PAGE and immunoblot showed that the pea catalase was composed of subunits of 57 kDa. Ultraviolet and visible absorption spectra of the enzyme showed two absorption maxima at 252 and 400 nm with molar extinction coefficients of 2.14 x 10(6) and 7.56 x 10(6) M(-1) cm(-1), respectively. By isoelectric focusing (pH 5-7), five different isoforms were identified and designated as CAT1-5, with isoelectric points of 6.41, 6.36, 6.16, 6.13 and 6.09, respectively. All the catalase isoforms contained a subunit of 57 kDa. Post-embedment, EM immunogold labelling of catalase showed a uniform distribution of the enzyme inside the matrix and core of pea leaf peroxisomes.
6-Phosphogluconate dehydrogenase (6PGDH) from rat-liver and kidney-cortex cytosol has been partially purified and almost completely isolated (more than 95%) from glucose-6-phosphate dehydrogenase activity. The purification and isolation procedures included high-speed centrifugation, 60-75% ammonium-sulphate fractionation, by which both hexose-monophosphate dehydrogenases activities were separated, and finally the protein fraction was applied to a chromatographic column of Sephadex G-25 equilibrated with 10 mM Tris-EDTA-NADP buffer, pH 7.6, to eliminate any contaminating metabolites. The kinetic properties of the isolated partially purified liver and renal 6PGDH were examined. The saturation curves of this enzyme in both rat tissues showed a typical Michaelis-Menten kinetic, with no evidence of co-operativity. The optimum pH for both liver and kidney-cortex 6PGDH was 8.0. The Km values of liver 6PGDH for 6-phosphogluconate (6PG) and for NADP were 157 microM and 258 microM respectively, while the specific activity measured at optimum conditions (pH 8.0 and 37 degrees C) was 424.2 mU/mg of protein. NADPH caused a competitive inhibition against NADP with an inhibition constant (Ki) of 21 microM. The Km values for 6PG and NADP from kidney-cortex 6PGDH were 49 microM and 56 microM respectively. The specific activity at pH 8.0 and 37 degrees C was 120.7 mU/mg of protein. NADPH also competitively inhibited 6PGDH activity, with a Ki of 41 microM. This paper describes a quick, easy and reliable method for the separation of the two dehydrogenases present in the oxidative segment of the pentose-phosphate pathway in animal tissues, eliminating interference in the measurements of their activities.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.